C＃Excel 2007错误

Response.Clear();
Response.AddHeader("content-disposition", "attachment;filename=cat5.xls");
Response.ContentEncoding = System.Text.Encoding.GetEncoding("windows-1254");
//Response.ContentEncoding = System.Text.Encoding.UTF7;
Response.Charset = "windows-1254";
//Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
Response.ContentType = "application/vnd.ms-excel";
Response.Cache.SetCacheability(HttpCacheability.NoCache);
System.IO.StringWriter stringWrite = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
GridView1.RenderControl(htmlWrite);
Response.Write(stringWrite.ToString());
Response.End();