Test.case
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<ext:ResourceManager ID="ResourceManager1" runat="server" />
<ext:ButtonGroup ID="ButtonGroup1" runat="server" Title="" Columns="3">
<Items>
<ext:SplitButton ID="SplitButton1" runat="server"
Text="Users" IconCls="add" IconAlign="Top"
ArrowAlign="Bottom" Width="60" Scale="Large" RowSpan="3">
<Listeners>
<Click Handler="#{Panel1}.load('TestCase2.aspx');" />
</Listeners>
</ext:SplitButton>
<ext:SplitButton ID="SplitButton2" runat="server"
Text="Users2" IconCls="add" IconAlign="Top"
ArrowAlign="Bottom" Width="60" Scale="Large" RowSpan="3">
<Listeners>
<Click Handler="#{Panel1}.load('TestCase3.aspx');" />
</Listeners>
</ext:SplitButton>
</Items>
</ext:ButtonGroup>
<ext:Panel ID ="Panel1" runat="server" Title="Loading on show">
<Loader ID="Loader1"
runat ="server"
Url =""
Mode ="Frame"
>
<LoadMask ShowMask="true" />
</Loader>
</ext:Panel>
</asp:Content>
TestCase2
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form2" runat="server">
here is the test case
</form>
</body>
</html>
TestCase3
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form3" runat="server">
here is the test case
</form>
</body>
</html>
*also u need to change form id of each loaded page as conflict happened.It is the key point I guess.(I tested and it works fine)