How to save the contents of a GridView to an excel spreadsheet

I am trying to save my GridView data as an Excel file.


Here's my code



 Response.Clear();
            Response.AddHeader("content-disposition", "attachment;filename=Report.xls");
           // Response.ContentType = "application/octet-stream";

            // If you want the option to open the Excel file without saving then
            // comment out the line below
            //Response.Cache.SetCacheability(HttpCacheability.NoCache);
            Response.ContentType = "application/vnd.xls";
            System.IO.StringWriter stringWrite = new System.IO.StringWriter();
            System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
           
            GridView3.RenderControl(htmlWrite);
         
            Response.Write(stringWrite.ToString());
            Response.End();

It doesn't work and I get a I get an error about Managed Pipelines. After changing it to Integrated, I still cant get it to work.

Regards.