private void UpdateConfig(string KeyName, string Xvalue)
        {
            XmlDocument doc = new XmlDocument();
            string sPath = Server.MapPath("web.config");
            doc.Load(sPath);
            XmlNode node = doc.SelectSingleNode(@"//add[@key='" + KeyName + "']");
            XmlElement ele = (XmlElement)node;
            ele.SetAttribute("value", Xvalue);
            doc.Save(sPath);
        }