string fs = @"C:\web.config";
            XmlDocument xmlDoc=new XmlDocument();
            xmlDoc.Load(fs);
            XmlNodeList nodeList=xmlDoc.SelectSingleNode("configuration").SelectSingleNode("CloverConfiguration").ChildNodes;
            foreach(XmlNode xn in nodeList)
            {
                try
                {
                    XmlElement xe=(XmlElement)xn;
                    if(xe.GetAttribute("key")=="Clover.DataAccess.ConnectionString")
                    {
                        xe.SetAttribute("value","server=server1;User ID=sa;Password=00000000;database=Clover;Connection Reset=FALSE");
                        break;
                    }
                }
                catch{}
            }
 
            xmlDoc.Save(fs);