protected void Button3_Click(object sender, EventArgs e)
        {
           Response.Clear();
　　       Response.Buffer= true;
　　       Response.Charset="utf-8";　　   
           Response.AppendHeader("Content-Disposition", "attachment;filename=FileFlow.xls");  
           Response.ContentEncoding = System.Text.Encoding.Default;     
           Response.ContentType = "application/ms-excel";
　　       this.EnableViewState = false;　                        
            oStringWriter = new ();
        System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);
           this.RenderControl(oHtmlTextWriter);
　　       Response.Write(oStringWriter.ToString());
　　       Response.End();
        }
调试显示RegisterForEventValidation can only be called during Render();的错误！
不知道为什么！请高手指教。