private void Log(string txt)
        {
            string logFile = Server.MapPath("/") + "log.txt";
 
            // create a writer and open the file
            TextWriter tw = new StreamWriter(logFile, true);
 
            // write a line of text to the file
            tw.WriteLine(DateTime.Now + " >> " + txt);
 
            // close the stream
            tw.Close();            
        }