Export to Excel not working for GridView inside UpdatePanel in ASP.Net

Hello Sir,

i have below code that i am using to export the Gridview data to excel sheet:

<%@ Page Language="C#" MasterPageFile="~/admin/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="admin_Default" Title="Untitled Page" EnableEventValidation="false"%>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc2" %>
 
<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
 
<%--<form id="form1" runat="server">--%>
 
 <cc2:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server" > </cc2:ToolkitScriptManager>
  
  <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
 
         <div style="padding-left:20px;line-height:1.5em;";>
              
             <div style="width:100%";>
                 
                <div style="float:right;margin-right:250px";>
      
     <asp:Button ID="Button1" runat="server" Text="Print Current Page" OnClick = "PrintCurrentPage" />

<asp:ImageButton ID="btn_export_list_to_excel" runat="server" 
            ImageUrl="../images/excel.jpg" AlternateText="Export List to Excel" 
            onclick="btn_export_list_to_excel_Click"/>
 </div>
                 
              </div>
             
             
             <asp:GridView ID="GridView1" runat="server"
AutoGenerateColumns = "false" Font-Names = "Arial"
Font-Size = "11pt" AlternatingRowStyle-BackColor = "#C2D69B" 
HeaderStyle-BackColor = "green" AllowPaging ="true"  
 DataKeyNames = "id" >
<Columns>
<asp:BoundField ItemStyle-Width = "150px" DataField = "id"
 HeaderText = "CustomerID" />
<asp:BoundField ItemStyle-Width = "150px" DataField = "name"
 HeaderText = "Name"/>
<asp:BoundField ItemStyle-Width = "150px" DataField = "school"
 HeaderText = "School"/>
</Columns>
</asp:GridView>
               
      <br />
    <br />
    <asp:Label ID="lbl_msg" runat="server" ForeColor="#0475BB" style="color: #0475BB;
    font-family: Arial;line-height: 27px;margin-left: 240px;margin-top: 90px;position: absolute;text-align: left;"></asp:Label>       
               
         </div>
             
    </ContentTemplate>
  </asp:UpdatePanel>
<%--</form>--%>
 
 
</asp:Content> 

Code behind code:

 protected void  btn_export_list_to_excel_Click(object sender, ImageClickEventArgs e)
    {
        Response.Clear();
        Response.Buffer = true;
        Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls");
        Response.Charset = "";
        Response.ContentType = "application/vnd.ms-excel";
        using (StringWriter sw = new StringWriter())
        {
            HtmlTextWriter hw = new HtmlTextWriter(sw);

            //To Export all pages
            GridView1.AllowPaging = false;
            ////this.BindGrid();
            this.grdview_search();

            GridView1.HeaderRow.BackColor = Color.White;
            foreach (TableCell cell in GridView1.HeaderRow.Cells)
            {
                cell.BackColor = GridView1.HeaderStyle.BackColor;
            }
            foreach (GridViewRow row in GridView1.Rows)
            {
                row.BackColor = Color.White;
                foreach (TableCell cell in row.Cells)
                {
                    if (row.RowIndex % 2 == 0)
                    {
                        cell.BackColor = GridView1.AlternatingRowStyle.BackColor;
                    }
                    else
                    {
                        cell.BackColor = GridView1.RowStyle.BackColor;
                    }
                    cell.CssClass = "textmode";
                }
            }

            GridView1.RenderControl(hw);

            //style to format numbers to string
            string style = @"<style> .textmode { } </style>";
            Response.Write(style);
            Response.Output.Write(sw.ToString());
            Response.Flush();
            Response.End();
        }
    }

But it is not working, please suggest the solution.

Regards
Rohit Sood