unable to export to excel

See more:

C#

ASP.NET

Javascript

Response.Clear();
       Response.AddHeader("content-disposition", string.Format("attachment;filename={0}.xls", fileName));
       Response.Charset = "";
       Response.Cache.SetCacheability(HttpCacheability.NoCache);
       Response.ContentType = "application/vnd.xls";
       StringWriter stringWrite = new StringWriter();
       HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
       grdGridView.RenderControl(htmlWrite);
       Response.Write(stringWrite.ToString());
       Response.Flush();
       Response.End();

Iam using above code to export excel..but there is a error at line

grdGridView.RenderControl(htmlWrite); 

says http exception was unhandled by user code
please help me with this