Excel e Asp.net

    protected void BtnExport_Click(object sender, ImageClickEventArgs e)
    {
        #region "Estrazione Nome File"
        string filename = "Export";
        #endregion

        Response.Clear();
        Response.AddHeader("content-disposition", "attachment;filename="+ filename +".xls");
        Response.Charset = "";
        Response.ContentType = "application/vnd.xls";

            #region "Estrazione Dati Grid Contratti"
            System.IO.StringWriter stringWrite = new System.IO.StringWriter();
            System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
            GridView dg = new GridView();
            dg = GridViewSheetContratti;
            dg.AllowSorting = false;
            dg.AllowPaging = false;
            dg.DataBind();
            dg.RenderControl(htmlWrite);
            Response.Write(stringWrite.ToString());
            #endregion

            #region "Estrazione Dati Grid Attività"
            System.IO.StringWriter stringWriteAtt = new System.IO.StringWriter();
            System.Web.UI.HtmlTextWriter htmlWriteAtt = new HtmlTextWriter(stringWriteAtt);
            GridView dgAtt = new GridView();
            dgAtt = GridViewSheetAttivita;
            dgAtt.AllowSorting = false;
            dgAtt.AllowPaging = false;
            dgAtt.DataBind();
            dgAtt.RenderControl(htmlWriteAtt);
            Response.Write(stringWriteAtt.ToString());
            #endregion

        Response.End();

    }
    public override void VerifyRenderingInServerForm(Control control)
    {
    }