Why modal popup extender is not showing?

I am using Visual Studio 2010 and for database I am using Entity Framework 4. 

The code runs without error but modal popup is not visible.

In my .aspx page I have the following:

<asp:ImageButton ID="edit" runat="server" CommandArgument='<%# Bind("EmpID")  %>' 
 CommandName="edituser" ImageUrl="image/images.jpg" ToolTip="Edit User Details" 
 OnClick="EditUser_Clicked"></asp:ImageButton><asp:ToolkitScriptManager ID="Toolkitmgr" runat="server"></asp:ToolkitScriptManager><asp:HiddenField ID="EmpID" runat="server" 
                 onvaluechanged="EmpID_ValueChanged"/><asp:ModalPopupExtender ID="mpedit" DropShadow="true" BackgroundCssClass="modalBackground"
                PopupControlID="pnedit"  CancelControlID="btnCancel"
                runat="server" TargetControlID="EmpID"></asp:ModalPopupExtender> <asp:Panel runat="server" ID="pnedit" CssClass="modalPopup" Style="display: block;width:525px">

           ***Some Code***

             </asp:Panel>

In the server side code for the EditUser_Clicked event I have the following:

 protected void EditUser_Clicked(object sender, EventArgs e)
        {
            ImageButton btndetails = sender as ImageButton;
            GridViewRow row = (GridViewRow)btndetails.NamingContainer;
            lblId.Text = GridView1.DataKeys[row.RowIndex].Value.ToString(); 
            name0.Text = row.Cells[1].Text;
            desig0.Text = row.Cells[2].Text;
            dob0.Text = row.Cells[3].Text;
            email0.Text = row.Cells[4].Text;
            country0.Text = row.Cells[5].Text;
            city0.Text = row.Cells[6].Text;
            add0.Text = row.Cells[7].Text;
            hq0.Text = row.Cells[8].Text;
            rbtnListGender0.Text = row.Cells[9].Text;
            mobno0.Text = row.Cells[10].Text;
            this.mpedit.Show();
        }

Thanks in advance.