The server control is taking a little longer than expected, so it's just easier to paste what I pass to the helper function. Sorry if it's a little messy. I'm in the process of revamping the app where I took the code from. Basically, in ExportGridView you pass the GridView control, the type of file you want exported, and a file name. It should work right off the bat, but if something is messed up let me know and I'll fix it.

  public enum ExportType
  {
   CSV, Excel, Word
  }

  private static void ClearControls(Control control)
  {
   for(int index = control.Controls.Count-1; index >= 0; index--)
   {
    ClearControls(control.Controls[index]);
   }

   if(!(control is TableCell))
   {
    if(control.GetType().GetProperty("SelectedItem") != null)
    {
     LiteralControl m_Literal = new LiteralControl();
     control.Parent.Controls.Add(m_Literal);

     m_Literal.Text = (string)control.GetType().GetProperty("SelectedItem").GetValue(control,null);
     control.Parent.Controls.Remove(control);
    }
    else
    {
     if(control.GetType().GetProperty("Text") != null)
     {
      LiteralControl m_Literal = new LiteralControl();
      control.Parent.Controls.Add(m_Literal);
      m_Literal.Text = (string)control.GetType().GetProperty("Text").GetValue(control,null);
      control.Parent.Controls.Remove(control);
     }
    }
   }
  }

  public static void ExportGridView(GridView gridView, string fileName, ExportType exportType)
  {
   const string m_Http_Attachment = "attachment;filename=";
   const string m_Http_Content = "content-disposition";

   HttpResponse m_Response = HttpContext.Current.Response;

   m_Response.Clear();
   m_Response.ClearContent();
   m_Response.ClearHeaders();
   m_Response.Buffer = true;

   m_Response.AddHeader(m_Http_Content, m_Http_Attachment + fileName);
   m_Response.ContentEncoding = Encoding.UTF8;
   m_Response.Cache.SetCacheability(HttpCacheability.NoCache);

   StringWriter m_StringWriter = new StringWriter();
   HtmlTextWriter m_HtmlWriter = new HtmlTextWriter(m_StringWriter);

   gridView.AllowPaging = false;
   gridView.HeaderStyle.Font.Bold = true;
   gridView.DataBind();

   ClearControls(gridView);
   gridView.RenderControl(m_HtmlWriter);

   string m_gridViewText = m_StringWriter.ToString();

   switch(exportType)
   {
    case ExportType.Excel:
     ExportHelper.ExportToExcelWord(m_gridViewText, "application/vnd.ms-excel", m_Response);
     break;

    case ExportType.CSV:
     ExportHelper.ExportToCsv(m_gridViewText, "application/csv", m_Response);
     break;

    case ExportType.Word:
     ExportHelper.ExportToExcelWord(m_gridViewText, "application/vnd.ms-word", m_Response);
     break;

    default:
     ExportHelper.ExportToExcelWord(m_gridViewText, "application/vnd.ms-excel", m_Response);
     break;
   }
  }