我的.net web页面中有个iframe,iframe加载了一个页面，里面有生成excel的功能，可是主窗口一点击就关闭了

请各位高手帮一下我的.net web页面中有个iframe,iframe加载了一个页面，里面有生成excel的功能，就是点击一个"生成execel"的按钮后，就会弹出让保存excel文件的对话框，可是一点击“保存”或“取消”主窗口就关闭了，请大家帮着看看这是怎么回事，这是代码:
 protected void Button2_Click(object sender, EventArgs e)
        {
           
            
            string excelName =DateTime.Now.Year+"年度" + Common.UtilCommon.ConvertToDoubleString(this.DropDownList1.SelectedValue) + "月份人员值班表.xls";
            if (this.GridView1.Rows.Count > 0)
                EmpExcel(excelName);
        }        private void EmpExcel(string excelName)
        {
            Response.Clear();
            Response.Buffer = true;
            Response.Charset = "gb2312";
            Response.AddHeader("content-disposition", "attachment;filename=" + HttpUtility.UrlEncode(excelName, Encoding.UTF8));
            Response.ContentEncoding = Encoding.GetEncoding("GB2312");
            Response.ContentType = "application/ms-excel";
            //System.Globalization.CultureInfo cul = new System.Globalization.CultureInfo("ZH-CN",true);
            StringWriter sw = new StringWriter();
            HtmlTextWriter htw = new HtmlTextWriter(sw);
            this.GridView1.RenderControl(htw);
            Response.Write(sw.ToString());
            Response.End();
        }