Response.TransmitFile(Server.MapPath("FilesConvert/") + file); Errror เมื่อกด next page ใน gridview

protected void GvFileResult_OnRowCommand(object sender, GridViewCommandEventArgs e)
        {
            string file = e.CommandArgument.ToString();
            Response.ClearContent();
            Response.Clear();
            Response.ContentType = "text/plain";
            Response.AddHeader("Content-Disposition", "attachment; filename=" + file + ";");
            Response.TransmitFile(Server.MapPath("FilesConvert/") + file); //Error
            Response.Flush();
            Response.End();

            Response.Write("<script>");
            Response.Write("alert('Success');");
            Response.Write("</script>");
        }