生成Excel文件

public static void GridViewToExcel(GridView gv, string excelName)
    {
        HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
        HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename=" + excelName + ".xls");        //关闭 ViewState
        //this.EnableViewState = false;
        System.IO.StringWriter tw = new System.IO.StringWriter();        System.Web.UI.HtmlTextWriter hw = new HtmlTextWriter(tw);
        //获取control的HTML
        gv.RenderControl(hw);
        //把HTML写回浏览器
        HttpContext.Current.Response.Write(tw.ToString());
        HttpContext.Current.Response.End();
        tw.Close();
        hw.Close();
    }
调用这个方法报错
错误如下：“/AlbumFoundation”应用程序中的服务器错误。
--------------------------------------------------------------------------------类型“GridView”的控件“GridView1”必须放在具有 runat=server 的窗体标记内。 
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。 异常详细信息: System.Web.HttpException: 类型“GridView”的控件“GridView1”必须放在具有 runat=server 的窗体标记内。源错误: 
行 296:        System.Web.UI.HtmlTextWriter hw = new HtmlTextWriter(tw);
行 297:        //获取control的HTML
行 298:        gv.RenderControl(hw);
行 299:        //把HTML写回浏览器
行 300:        HttpContext.Current.Response.Write(tw.ToString());
 源文件: d:\Projects\AlbumFoundation.root\AlbumFoundation\WebSites\AlbumFoundation\orders\OrderExpiredata.aspx.cs    行: 298 堆栈跟踪: 
[HttpException (0x80004005): 类型“GridView”的控件“GridView1”必须放在具有 runat=server 的窗体标记内。]
   System.Web.UI.Page.VerifyRenderingInServerForm(Control control) +8693171
   System.Web.UI.WebControls.GridView.Render(HtmlTextWriter writer, Boolean renderPanel) +40
   System.Web.UI.WebControls.GridView.Render(HtmlTextWriter writer) +33
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +99
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   orders_OrderExpiredata.GridViewToExcel(GridView gv, String excelName) in d:\Projects\AlbumFoundation.root\AlbumFoundation\WebSites\AlbumFoundation\orders\OrderExpiredata.aspx.cs:298
   orders_OrderExpiredata.btnExcel_Click(Object sender, EventArgs e) in d:\Projects\AlbumFoundation.root\AlbumFoundation\WebSites\AlbumFoundation\orders\OrderExpiredata.aspx.cs:327
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565