Losing file in a file upload control in update panel c# asp.net

Question

I have a page where I am using 3 update panels and all the update panels are working well. In one of the update panels, I have a button which on click changes label text but the problem is that on if post back happens in any of the update panels file upload loses its file.

All the update panels are used to update separate sections of page. No update panel is nested. The file upload is outside; it is not in any of the update panels but it is still losing its file.

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="WalkInControl.ascx.cs"
    Inherits="Modules_WalkInControl" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajaxtoolkit" %>

 <asp:Panel ID="Panel1" runat="server" Font-Size="13px" Width="670">
 <asp:UpdatePanel ID="UpdatePanel1" runat="server" ChildrenAsTriggers ="true"  UpdateMode="Conditional">
    <ContentTemplate>

            <div class="formfieldset" style="margin-bottom: 40px;">
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Check In :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtCheckIn" runat="server" Width="153px"></asp:TextBox>
                        <asp:ImageButton ID="imgbtnCalendar1" runat="server" ImageUrl="~/App_Themes/Default/images/ico-calendar.gif"
                            CausesValidation="false" Width="20" Height="20" />
                        <ajaxtoolkit:CalendarExtender ID="CalendarExtender2" runat="server" Format="dd/MM/yyyy"
                            TargetControlID="txtCheckIn" PopupButtonID="imgbtnCalendar1" />
                    </div>
                    <div class="paymentfrmvalidation">
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="[*]"
                            ControlToValidate="txtCheckIn" Display="Dynamic" ValidationGroup="a"></asp:RequiredFieldValidator>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Check Out:
                    </div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtCheckOut" runat="server" Width="153px"></asp:TextBox>
                        <asp:ImageButton ID="imgbtnCalendar" runat="server" ImageUrl="~/App_Themes/Default/images/ico-calendar.gif"
                            CausesValidation="false" ImageAlign="Top" Width="20" Height="20" />
                        <ajaxtoolkit:CalendarExtender ID="CalendarExtender1" runat="server" Format="dd/MM/yyyy"
                            TargetControlID="txtCheckOut" PopupButtonID="imgbtnCalendar" />
                    </div>
                    <div class="paymentfrmvalidation">
                        <asp:RequiredFieldValidator ID="valStartDate" runat="server" ErrorMessage="[*]" ControlToValidate="txtCheckOut"
                            Display="Dynamic" ValidationGroup="a"></asp:RequiredFieldValidator>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Room Type :
                    </div>
                    <div class="paymentfrmtxtbox">
                        <asp:DropDownList ID="drpRoomtype" runat="server" Width="172px" AutoPostBack="True"
                            OnSelectedIndexChanged="drpRoomtype_SelectedIndexChanged" AppendDataBoundItems="True">
                        </asp:DropDownList>
                    </div>
                </div>
                  <div class="formrow">
                <div class="paymentfrmlabels">
                   Plan :
                </div>
                <div class="paymentfrmtxtbox" style="height: 25px;">

                    <asp:DropDownList ID="drpPlan" Width="172px" AutoPostBack="True"  
                        runat="server" onselectedindexchanged="drpPlan_SelectedIndexChanged1">
                    </asp:DropDownList>
                </div>
            </div>
                <div class="formrow" style="height: 75px;">
                    <div class="paymentfrmlabels">
                        Room :
                    </div>
                    <div class="paymentfrmtxtbox">
                        <asp:ListBox ID="lstRooms" runat="server" Width="172px" SelectionMode="Multiple">
                        </asp:ListBox>
                    </div>
                    <div class="paymentfrmvalidation">
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="lstRooms"
                            ErrorMessage="[*]" ValidationGroup="b"></asp:RequiredFieldValidator>
                    </div>
                    <div class="paymentfrmvalidation">
                        <asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1">
                            <ProgressTemplate>
                                <img src="../Images/loading_sm.gif" border="0" alt="">
                            </ProgressTemplate>
                        </asp:UpdateProgress>
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="drpRoomtype"
                            ErrorMessage="[*]" ValidationGroup="a"></asp:RequiredFieldValidator>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Adults :
                    </div>
                    <div class="paymentfrmtxtbox" style="width: 50px; height: 25px;">
                        <asp:DropDownList ID="drpAdults" Width="50px" runat="server" AutoPostBack="True"
                            OnSelectedIndexChanged="drpAdults_SelectedIndexChanged" AppendDataBoundItems="True">
                        </asp:DropDownList>
                    </div>
                    <div class="paymentfrmlabels" style="width: 65px;">
                        Children :
                    </div>
                    <div class="paymentfrmtxtbox" style="width: 50px; height: 25px;">
                        <asp:DropDownList ID="drpChildren" Width="50px" runat="server" AutoPostBack="True"
                            OnSelectedIndexChanged="drpChildren_SelectedIndexChanged">
                        </asp:DropDownList>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Rate :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtRate" Width="153px" runat="server"></asp:TextBox>
                    </div>
                    <div class="paymentfrmvalidation">
                        <%--<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="txtRate"
                            ErrorMessage="Invalid Format" ValidationExpression="^(-)?\d+(\.\d\d)?$" ValidationGroup="a"></asp:RegularExpressionValidator>
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ControlToValidate="txtRate"
                            ErrorMessage="Rate Required" ValidationGroup="a"></asp:RequiredFieldValidator></div>--%>

                    </div>

                </div> <div align="center"> <asp:Label ID="lblRoomMsg" runat="server" ForeColor="Red"></asp:Label></div>
                 <div class="formrow">
                    <div class="paymentfrmlabels">
                        Advance Pay:
                    </div>
                    <div class="paymentfrmtxtbox" style="height: 25px;">
                        <asp:TextBox ID="txtAdvance" runat="server" Width="153px">0.0</asp:TextBox>
                    </div>
                </div>
                <div class="formrow" style="text-align: right;">
                    <asp:LinkButton ID="lnkAdd" CssClass="btn" runat="server" Width="60px" OnClick="lnkAdd_Click1">ADD</asp:LinkButton>
                </div>


                <div class="formrow" style="text-align:center;">
             <asp:CompareValidator ID="CompareValidator1" runat="server"  ControlToCompare="txtCheckOut"
                ControlToValidate="txtCheckIn" Operator="LessThanEqual" Type="Date" ForeColor="Red"    ErrorMessage="CheckIn Must Be Before CheckOut" 
                Display="Dynamic" ValidationGroup="a"/>

             </div> 
               <div class="formrow" style="height: auto; margin-top: 20px; width: 430px;">
                    <asp:GridView ID="gvAddedRooms" runat="server" CssClass="active-grid" AutoGenerateColumns="False"
                        DataKeyNames="ID" Height="18px" Width="100%" OnRowDeleting="gvAddedRooms_RowDeleting">
                        <Columns>
                            <asp:BoundField DataField="ID" HeaderText="ID" />
                            <asp:BoundField DataField="RoomTypeX" HeaderText="RoomType" />
                                <asp:BoundField DataField="RoomX" HeaderText="RoomX" />
                            <asp:BoundField DataField="Rate" HeaderText="Rate" DataFormatString="{0:f}" />
                            <asp:BoundField DataField="Adults" HeaderText="Adults" />
                            <asp:BoundField DataField="Children" HeaderText="Children" />
                            <asp:CommandField ShowDeleteButton="True" />
                        </Columns>
                    </asp:GridView>

                </div>
               <div style="float:left;"> <asp:Label ID="Label1" runat="server" Text="Total Charge : " Font-Bold="true" ForeColor ="Blue" style="font-size:19px;"></asp:Label><asp:Label ID="lblTotalAmount" runat="server" Text=""></asp:Label>
                </div>


            </ContentTemplate>
             <Triggers>
             <asp:PostBackTrigger ControlID="gvAddedRooms" />
                                <asp:PostBackTrigger ControlID="drpRoomtype" />
                                <asp:PostBackTrigger ControlID="drpPlan"  />
                                <asp:PostBackTrigger ControlID="lnkAdd"   />
                                <asp:PostBackTrigger ControlID="lstRooms" />
                                   <asp:PostBackTrigger ControlID="drpAdults"   />
                                <asp:PostBackTrigger ControlID="drpChildren" />

                 <asp:PostBackTrigger ControlID="btnRemoveFilename1" />
                            </Triggers>


            </asp:UpdatePanel> 

              <%--<div class="formrow" style="text-align: right;">

             <asp:UpdatePanel ID="UpdatePanel3"  UpdateMode ="Conditional"  runat="server">
                <ContentTemplate >
                      Agency : 
                      <asp:DropDownList ID="drpChannel" runat="server" Width="172px" AutoPostBack="True"
                         Height="32px" >
                    </asp:DropDownList>  
                      </ContentTemplate>
                     <Triggers>
                                 <asp:PostBackTrigger ControlID="drpChannel" 
                                      />
                                <asp:AsyncPostBackTrigger ControlID="lnkNewChannel" EventName="Click" />

                               </Triggers>
                </asp:UpdatePanel>
                       <asp:LinkButton ID="lnkNewChannel" runat="server" >New Channel</asp:LinkButton>
                       </div> --%> 



             <div class="newsubheadingsearchqueryresults" style="width: 685px;">
                <h3>
                    Customer Details</h3>
                <span class="requiredExample">[&nbsp;*&nbsp;] = Required Information</span></div>
            <div class="formfieldset" style="margin-bottom: 40px;">
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Paying Customer :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtCustomerName" Width="153px" runat="server"></asp:TextBox>
                    </div>
                    <div class="paymentfrmvalidation">
                        <asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server" ControlToValidate="txtCustomerName"
                            ErrorMessage="[*]" ValidationExpression="^[a-zA-Z''-'\s]{1,40}$" 
                            ValidationGroup="a" Display="Dynamic"></asp:RegularExpressionValidator>
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ControlToValidate="txtCustomerName"
                            ValidationGroup="a" ErrorMessage="[*]" Display="Dynamic"></asp:RequiredFieldValidator>
                    </div>
                </div>

                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Customer Type :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:DropDownList ID="drpCustomerType" Width="153px" runat="server">
                            <asp:ListItem Text="Person" Value="Person"></asp:ListItem>
                            <asp:ListItem Text="Company" Value="Company"></asp:ListItem>
                        </asp:DropDownList>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        E-Mail :
                    </div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtEmail" Width="153px" runat="server"></asp:TextBox>
                    </div>
                    <div class="paymentfrmvalidation">
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Phone No :
                    </div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtPhone" runat="server" Height="23px" Width="153px"></asp:TextBox>
                    </div>
                    <div class="paymentfrmvalidation">
                        <asp:RegularExpressionValidator ID="RegularExpressionValidator4" runat="server" ErrorMessage="Invalid format"
                            Display="Dynamic" ValidationExpression="^[0-9]*$" ControlToValidate="txtPhone"
                            ValidationGroup="a"></asp:RegularExpressionValidator>
                        <asp:RequiredFieldValidator ID="RequiredFieldValidator6" runat="server" ControlToValidate="txtPhone"
                            Display="Dynamic" ValidationGroup="a" ErrorMessage="[*]"></asp:RequiredFieldValidator>
                    </div>
                </div>
                <div class="formrow" style="height: 130px;">
                    <div class="paymentfrmlabels">
                        Address:</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtAddress" runat="server" Height="129px" TextMode="MultiLine" Width="153px"></asp:TextBox>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        City :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtCity" runat="server" Width="153px"></asp:TextBox>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        Country :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:DropDownList ID="drpCountry" Width="153px" runat="server">
                        </asp:DropDownList>
                    </div>
                </div>
                <div class="formrow">
                    <div class="paymentfrmlabels">
                        State :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtState" Width="153px" runat="server"></asp:TextBox>
                    </div>
                </div>
                 <div class="formrow">
                    <div class="paymentfrmlabels">
                        Postal Code :</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtPostalCode" Width="153px" runat="server"></asp:TextBox>
                    </div>
                </div>

                <div class="formrow" style="height: 90px; width: 670px;">
                    <div class="paymentfrmlabels">
                        Other Guest Names :</div>
                    <div class="paymentfrmtxtbox" style="margin-right:45px;">
                        <asp:TextBox ID="txtOtherGuest" runat="server" Height="90px" Width="153px" TextMode="MultiLine"></asp:TextBox>
                    </div>
                    <div class="paymentfrmlabels">
                        Other Information:</div>
                    <div class="paymentfrmtxtbox">
                        <asp:TextBox ID="txtOtherInf" runat="server" Height="90px" Width="153px" TextMode="MultiLine"></asp:TextBox>
                    </div>
                </div>



                <div class="formrow" style="vertical-align: text-top;">
                    <div class="paymentfrmlabels">
                        Identity Proof :</div>


                </div>

                <div class="formrow">
                    <div class="paymentfrmtxtbox">
                    </div>
                </div>
                <div class="formrow" style="text-align: right">
                    <div class="paymentfrmlabels">
                      <input id="txtLogoFileName1" type="file" style ="float :left; z-index:999;" name="txtSmallImage1FileName" runat="server" />

                        <asp:UpdatePanel ID="UpdatePanel2" runat="server" ChildrenAsTriggers ="true"  UpdateMode ="Conditional">
                        <ContentTemplate >
                          <div class="paymentfrmtxtbox">
                       <asp:Button ID="btnRemoveFilename1" runat="server" style="margin-left:50px; float :left; z-index:999;" Text="Remove" OnClick="btnRemoveFilename1_Click">
                        </asp:Button>
                       </div>
                        <asp:Label ID="lblLogoFileName1" runat="server" CssClass="labelText" ForeColor="Silver"> </asp:Label>

                </div>
                 </ContentTemplate>
                         <Triggers >
                         <asp:PostBackTrigger ControlID ="btnRemoveFilename1" />
                         </Triggers>   
                        </asp:UpdatePanel> 
                <div class="formrow" style="width: 300px;">
                   <div class="paymentfrmtxtbox ">
                       <asp:UpdatePanel ID="UpdatePanel3"  UpdateMode ="Conditional"   ChildrenAsTriggers ="true" runat="server">
                <ContentTemplate >
                      Agency: &nbsp;&nbsp;&nbsp;
                      <asp:DropDownList ID="drpChannel" runat="server" Width="153px" AutoPostBack="True"
                         style=" float: right; height: 28px; margin-right: 65px;width: 157px;" >
                    </asp:DropDownList>  
                      </ContentTemplate>
                     <Triggers>
                                 <asp:PostBackTrigger ControlID="drpChannel" 
                                      />
                                <asp:AsyncPostBackTrigger ControlID="lnkNewChannel" EventName="Click" />

                               </Triggers>
                </asp:UpdatePanel>
                       <asp:LinkButton ID="lnkNewChannel" runat="server" style="display:block; float: right;margin-right: -71px; margin-top: 16px;" >New Channel</asp:LinkButton>

                    </div>
                    </div>

                </div>



                <div class="formrow" style="text-align: right; font-weight:bold; color:#000;">

                 </div>








                <div class="formrow" style="text-align: right; width: 670px;">
                    <asp:LinkButton ID="lnkSubmit" CssClass="btn" runat="server" OnClick="lnkSubmit_Click1"
                        Width="65px" ValidationGroup="a">Check In</asp:LinkButton>
                    <asp:LinkButton ID="lnkCheckout" CssClass="btn" Width="65px" runat="server" OnClick="lnkCheckout_Click"
                        ValidationGroup="a">Check Out</asp:LinkButton>
                    <asp:LinkButton ID="lnkCancel" CssClass="btn" Width="65px" runat="server" OnClick="lnkCancel_Click1">Cancel</asp:LinkButton>
                </div>
            </div>
             </div>

            <ajaxtoolkit:ModalPopupExtender ID="ModalPopupExtender1"   BackgroundCssClass="modalBackground" PopupControlID ="pnlChannel" TargetControlID ="lnkNewChannel" CancelControlID ="ImgBtnClose" runat="server">
            </ajaxtoolkit:ModalPopupExtender>


        <asp:Panel ID="pnlChannel" runat="server">
        <div align="right" style ="padding-top :50px" >
           <asp:ImageButton ID="ImgBtnClose" width="25px" Height ="25px" ImageUrl="~/Images/cross.png" runat="server" /></div>
           <div style ="background-color:White ; border :20px; border-color:Blue;padding:20px 40px; border-radius:20px;" >




                <style type="text/css">
    .style1 {
        width: 100%;
    }
    .style2
    {
        text-align: center;
        font-weight: bold;
        font-family: Andalus;
        font-size: xx-large;
        color: #434343;
    }
    .style3
    {
        width: 81px;
    }
</style>
<div>
<table class="style1">
    <tr>
        <td class="style2" colspan="2">
          Agency</td>
    </tr>
      <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
        <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
    <tr>
        <td class="style3">
            <asp:Label ID="lblName" runat="server" Text="Name:"></asp:Label>
        </td>
        <td>
            <asp:TextBox ID="txtName" runat="server" Width="189px"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidator5" runat="server" 
                ControlToValidate="txtName" Display="Dynamic" ErrorMessage="Mandatory Field!!!" 
                ForeColor="Red" ValidationGroup="acssd23"></asp:RequiredFieldValidator>
            <asp:RegularExpressionValidator ID="RegularExpressionValidator5" runat="server" 
                ControlToValidate="txtName" Display="Dynamic" 
                ErrorMessage="Invalid Name Format!!!" Font-Names="Arial" Font-Size="8pt" 
                ForeColor="Red" SetFocusOnError="True" 
                ValidationExpression="^[a-zA-Z-'.\s]{1,50}" ValidationGroup="acssd23"></asp:RegularExpressionValidator>
        </td>
    </tr>
    <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
    <tr>
        <td class="style3">
            <asp:Label ID="lblContact" runat="server" Text="Contact:"></asp:Label>
        </td>
        <td>
            <asp:TextBox ID="txtContact" runat="server" Width="189px"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidator7" runat="server" 
                ControlToValidate="txtContact" Display="Dynamic" 
                ErrorMessage="Mandatory Field!!!" ForeColor="Red" 
                ValidationGroup="acssd23"></asp:RequiredFieldValidator>
            <asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" 
                ControlToValidate="txtContact" Display="Dynamic" 
                ErrorMessage="Invalid Contact Format!!!" ForeColor="Red" 
                style="font-size: xx-small" ValidationExpression="^[0-9-+]*$" 
                ValidationGroup="acssd23"></asp:RegularExpressionValidator>
        </td>
    </tr>
      <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
    <tr>
        <td class="style3">
            <asp:Label ID="lblAddress" runat="server" Text="Address:"></asp:Label>
        </td>
        <td>
            <asp:TextBox ID="txtAddresss" runat="server" Height="64px" TextMode="MultiLine" 
                width="189px"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidator8" runat="server" 
                ControlToValidate="txtAddresss" Display="Dynamic" 
                ErrorMessage="Mandatory Field!!!" ForeColor="Red" 
                ValidationGroup="acssd23"></asp:RequiredFieldValidator>
        </td>
    </tr>
      <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
    <tr>
        <td class="style3">
            <asp:Label ID="lblEmail" runat="server" Text="Email:"></asp:Label>
        </td>
        <td>
            <asp:TextBox ID="txtEmails" runat="server" Width="189px"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" 
                ControlToValidate="txtEmails" Display="Dynamic" 
                ErrorMessage="Mandatory Field!!!" ForeColor="Red" 
                ValidationGroup="acssd23"></asp:RequiredFieldValidator>
            <asp:RegularExpressionValidator ID="RegularExpressionValidator015" runat="server" 
                ControlToValidate="txtEmail" ErrorMessage="Invalid Email Format!!!" 
                ForeColor="Red" 
                ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" 
                ValidationGroup="acssd23"></asp:RegularExpressionValidator>
        </td>
    </tr>
      <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
    <tr>
        <td class="style3">
            <asp:Label ID="lblWebsite" runat="server" Text="Website:"></asp:Label>
        </td>
        <td>
            <asp:TextBox ID="txtWebsite" runat="server" Width="189px"></asp:TextBox>
        </td>
    </tr>
          <tr><td>&nbsp;</td><td>&nbsp;</td></tr>
    <tr>
        <td class="style3">
            &nbsp;</td>
        <td>
            &nbsp;</td>
    </tr>

    <tr>
        <td class="style3">
            &nbsp;</td>
        <td align ="right" >
            <asp:Button ID="btnSubmit" CssClass="btn" Width ="140px" runat="server" Text="Submit" 
                onclick="btnSubmit_Click" style="height: 26px" ValidationGroup="acssd23" />
        </td>
    </tr>
</table>
</div>




</div>
        </asp:Panel>
           </asp:Panel>

Answer 1

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true" />
    <div>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="conditional">
            <Triggers>
                <asp:PostBackTrigger ControlID="Button1" />
            </Triggers>
            <ContentTemplate>
                 <asp:FileUpload ID="FileUpload1" runat="server" />
                 <asp:Button ID="Button1" runat="server"Text="Upload" OnClick="Button1_Click" />
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>

Answer 2

The default ASP.NET FileUpload control will never work with an UpdatePanel. You need a special AsyncFileUpload control as defined in an AjaxControl Toolkit.

<ajaxToolkit:AsyncFileUpload OnClientUploadError="uploadError"
     OnClientUploadComplete="uploadComplete" runat="server"
     ID="AsyncFileUpload1" Width="400px" UploaderStyle="Modern"
     UploadingBackColor="#CCFFFF" ThrobberID="myThrobber" />

or you can use UpdatePanel Triggers

<Triggers>
  <asp:PostBackTrigger ControlID="YourControlID" />
</Triggers>

Answer 3

I spent all afternoon on this today, using any number of solutions I found on various forums, including this one, CodeProject.com, asp.net forums, and a whole slew of others. I tried setting Postback triggers and AsyncPostback triggers, and this late at night I can't remember what all else. None of them worked, including the one marked as the answer on this page. What I finally found was an obscure post from 2007 on the asp.net forum which, for some reason now will not load on my browser. At any rate, what finally worked for me was replacing the

<form id="form1" runat="server>

tag with this:

<form id="Form1" method="post" enctype="multipart/form-data" runat="server">

Worked beautifully.

In my case it was in the Site.Master file, but in the case of the posting on forums.asp.net, it worked in a default.aspx file.

Update: The forums.asp.net site was down, but it's back up now: UpdatePanel + FileUpload + PostBackTrigger doesn't seem to work.