protected void btnDownload_Click(object sender, EventArgs e)
 {
     try
     {
         Response.Clear();
         Response.AddHeader("content-disposition", "attachment;filename=Report.xls");
         Response.ContentType = "application/vnd.xls";
         System.IO.StringWriter       stringWrite = new System.IO.StringWriter();
         System.Web.UI.HtmlTextWriter htmlWrite   = new HtmlTextWriter(stringWrite);
         GvTech.RenderControl(htmlWrite);
         Response.Write(stringWrite.ToString());
         Response.End();
     }
     catch (Exception ex)
     {
         throw ex;
     }
 }