Edit ASP.Net GridView row using ASP.Net AJAX ModalPopupExtender in C# and VB.Net

Hello,

I can't pass a gridview commandargument to the popup ajax ModalPopupExtender when I try to edit event.

Can you help me?

My code below

<asp:TemplateField ItemStyle-HorizontalAlign="Center">
    <ItemTemplate>
        <asp:ImageButton ID="btnedit" runat="server" CommandName="Edit"
             CommandArgument='<%# Eval("tkt") %>' ImageUrl="/aspnet/img/edit_icon.gif" />
    </ItemTemplate>
</asp:TemplateField>

protected void gvProducts_RowEditing(object sender, GridViewEditEventArgs e)
{
    ModalPopupExtender1.Show();
    Button btn = (Button)sender;
    string t = btn.CommandArgument.ToString();
    Response.Write(t);
}

Error

Unable to cast object of type 'System.Web.UI.WebControls.GridView' to type 'System.Web.UI.WebControls.Button'.