Getting Error While exporting data from gridview to excel...

public static void ExportToExcel(string strFileName, GridView dg)
   {
       try
       {
           HttpContext.Current.Response.ClearContent();
           int row = dg.Rows.Count;
           HttpContext.Current.Response.AddHeader("content-disposition", "attachment; filename=" + strFileName + System.DateTime.Now.Hour + "_" + System.DateTime.Now.Minute + ".xls");
           HttpContext.Current.Response.ContentType = "application/excel";
           System.IO.StringWriter sw = new System.IO.StringWriter();
           HtmlTextWriter htw = new HtmlTextWriter(sw);
           dg.RenderControl(htw);
           HttpContext.Current.Response.Write(sw.ToString());
           HttpContext.Current.Response.End();
           HttpContext.Current.ApplicationInstance.CompleteRequest();
           return;
       }
       catch(Exception ex)
       {
           //ex.Message();
       }
   }

public override void VerifyRenderingInServerForm(Control control)
   {
       /* Verifies that the control is rendered */
   }

AutoEventWireup="true" EnableEventValidation="false"

This is a common error , you need to override VerifyRenderingInServerForm Method,

http://aspalliance.com/771