dear sir, I am writing one program editing in grid view pop up.i have used ajax tool kit.But some problem Generate.Problem is 
0x800a1391 - Microsoft JScript runtime error: 'Sys' is undefined.My code is Below.
 
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Forward.aspx.cs" Inherits="WebApplication2.Forward" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Untitled Page</title>
<style type="text/css">
.modalBackground
{
background-color: Gray;
z-index: 10000;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<asp:ToolkitScriptManager ID="ScriptManager1" runat="server">
   
</asp:ToolkitScriptManager>
<div>
<asp:GridView runat="server" ID="gvdetails" DataKeyNames="ID" AutoGenerateColumns="false">
<RowStyle BackColor="#EFF3FB" />
<FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
<HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
<AlternatingRowStyle BackColor="White" />
<Columns>
<asp:TemplateField HeaderText="Edit">
<ItemTemplate>
<asp:ImageButton ID="imgbtn" ImageUrl="images/bg1.jpg"  runat="server" Width="25" Height="25" onclick="imgbtn_Click" />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="ID" HeaderText="ID" />
<asp:BoundField DataField="Sender" HeaderText="Sender" />
<asp:BoundField DataField="reciver" HeaderText="Reciver" />
</Columns>
</asp:GridView>
<asp:Label ID="lblresult" runat="server"/>
<asp:Button ID="btnShowPopup" runat="server" style="display:none" />
<asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="btnShowPopup" PopupControlID="pnlpopup"
CancelControlID="btnCancel" BackgroundCssClass="modalBackground">
</asp:ModalPopupExtender>
<asp:Panel ID="pnlpopup" runat="server" BackColor="White" Height="269px" Width="400px" style="display:none">
<table width="100%" style="border:Solid 3px #D55500; width:100%; height:100%" cellpadding="0" cellspacing="0">
<tr style="background-color:#D55500">
<td colspan="2" style=" height:10%; color:White; font-weight:bold; font-size:larger" align="center">User Details</td>
</tr>
<tr>
<td  style=" width:45%">
ID:
</td>
<td>
<asp:Label ID="lblID" runat="server"></asp:Label>
</td>
</tr>
<tr>
<td>
Name:
</td>
<td>
<asp:Label ID="lblusername" runat="server"></asp:Label>
</td>
</tr>
<tr>
<td >
Designation:
</td>
<td>
<asp:TextBox ID="txtDesg" runat="server"/>
</td>
</tr>
<tr>
<td>
</td>
<td>
<asp:Button ID="btnUpdate" CommandName="Update" runat="server" Text="Update" onclick="btnUpdate_Click"/>
<asp:Button ID="btnCancel" runat="server" Text="Cancel" />
</td>
</tr>
</table>
</asp:Panel>
  
</div>
</form>
</body>
</html>
 aspx.xs page is below
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using AjaxControlToolkit;
namespace WebApplication2
{
    public partial class Forward : System.Web.UI.Page
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["CON"].ToString());
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindGridData();
            }
        }
        protected void BindGridData()
        {
            con.Open();
            SqlCommand cmd = new SqlCommand("Select id,sender,reciver from inbox", con);
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            da.Fill(dt);
            gvdetails.DataSource = dt;
            gvdetails.DataBind();
        }
        protected void btnUpdate_Click(object sender, EventArgs e)
        {
            //con.Open();
            //SqlCommand cmd = new SqlCommand("update Table_1 set Name=@Name,Designation=@Designation where ID=@ID", con);
            //cmd.Parameters.AddWithValue("@Name", lblusername.Text);
            //cmd.Parameters.AddWithValue("@Designation", txtDesg.Text);
            //cmd.Parameters.AddWithValue("@ID", Convert.ToInt32(lblID.Text));
            //cmd.ExecuteNonQuery();
            //con.Close();
            //lblresult.Text = lblusername.Text + " Details Updated Successfully";
            //lblresult.ForeColor = Color.Green;
            //BindGridData();
        }
        protected void imgbtn_Click(object sender, ImageClickEventArgs e)
        {
            ImageButton btndetails = sender as ImageButton;
            GridViewRow gvrow = (GridViewRow)btndetails.NamingContainer;
            lblID.Text = gvdetails.DataKeys[gvrow.RowIndex].Value.ToString();
            lblusername.Text = gvrow.Cells[2].Text;
            txtDesg.Text = gvrow.Cells[3].Text;
            this.ModalPopupExtender1.Show();
        }
    }
}