从girdview输出到excel中的问题

Response.Clear();
            Response.Buffer = true;
            Response.Charset = "GB2312";
            Response.AppendHeader("Content-Disposition", "attachment;filename=FileName.xls");
            Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");//设置输出流为简体中文
            Response.ContentType = "application/ms-excel";//设置输出文件类型为excel文件。 
            this.EnableViewState = false;
            System.Globalization.CultureInfo myCItrad = new System.Globalization.CultureInfo("ZH-CN", true);
            System.IO.StringWriter oStringWriter = new System.IO.StringWriter(myCItrad);
            System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);
            this.LCD_GridView.RenderControl(oHtmlTextWriter);
            Response.Write(oStringWriter.ToString());
            Response.End();报的错误是“类型“GridView”的控件“LCD_GridView”必须放在具有 runat=server 的窗体标记内。”
但是我的GridView的确是放在runat=server 的窗体标记中了，要不我的GridView怎么能显示数据呢
这是怎么回事啊？