在将GridView导出EXCEL，打开时，提示不能读取文件
 代码如下：
     Report report = new Report();
        System.Data.DataTable  dt = report.Get_Settlement_Searching_History(fromdate, todate, customer_code, source).Tables[0];
        this.GridView1.DataSource = dt;
        this.GridView1.DataBind();

          Response.Charset = "GB2312";
        Response.ContentEncoding = System.Text.Encoding.UTF7;
        Response.AppendHeader("Content-Disposition", "attachment;filename=" +    HttpUtility.UrlEncode("Settlement_Searching_History.xls", System.Text.Encoding.UTF8).ToString());
        Response.ContentType = "application/ms-excel";
        this.EnableViewState = false;

        StringWriter tw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(tw);
        GridView1.RenderControl(hw);
        Response.Write(tw.ToString());
        Response.Flush();
        Response.End();
    public override void VerifyRenderingInServerForm(Control control) { }

 希望帮忙解决下。先谢了。