AutoCompleteExtender suddenly stopped working

Question

I have implemented AjaxControlToolkit AutoCompleteExtender in one of my projects and it was working fine. Suddenly one day when I opened the project, AutoCompleteExtender stopped working. All other features of the Toolkit like calendar control are working fine.

To investigate the issue, I tried creating a new web application and copied the same code in the new application but it worked fine. Can sombody help with this.

I am using version 4.1.50731 of AjaxControlToolkit and below is the code I have written.

Register Assembly:

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

Aspx Page:

<form id="form1" runat="server">
    <div>
        <span class="span-formitem">
            <asp:Label ID="lblName" runat="server" Text="Name"></asp:Label><br />
            <cc1:ToolkitScriptManager runat="server" ID="ToolkitScriptManager1" EnablePageMethods="true"></cc1:ToolkitScriptManager>
            <asp:TextBox ID="txtName" runat="server"></asp:TextBox>
            <cc1:AutoCompleteExtender ServiceMethod="SearchEmployees"
                MinimumPrefixLength="3"
                CompletionInterval="100" EnableCaching="false" CompletionSetCount="10"
                TargetControlID="txtName"
                ID="AutoCompleteExtender1" runat="server" FirstRowSelected="false">
            </cc1:AutoCompleteExtender>
        </span>
    </div>
</form>

Code for getting the data:

[System.Web.Script.Services.ScriptMethod()]
[System.Web.Services.WebMethod()]
public static List<string> SearchEmployees(string prefixText, int count)
{
    using (SqlConnection conn = new SqlConnection())
    {
        conn.ConnectionString = "Data Source=dd-SQL21;Database=CMCM;User ID=CMCM;Password=xx@12xx";

        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = "select top 15 employeename" + " from employee_master" + " where employeename like '%" + prefixText + "%'" +
                " order by (case when employeename like '" + prefixText + "%' then 1" + " when employeename like '% " + prefixText + "%' then 2" +
                    " else 3" + " end);";
            cmd.Parameters.AddWithValue("@SearchText", prefixText);
            cmd.Connection = conn;
            conn.Open();
            List<string> employees = new List<string>();
            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                while (sdr.Read())
                {
                    employees.Add(sdr["employeename"].ToString());
                }
            }
            conn.Close();
            return employees;
        }
    }
}