function handleHTTPerror(errorNumber, descriptionString) {
      var message = '';
      switch(errorNumber) {
          case 400:
              message = message + 'HTTP ERROR 400: (' + descriptionString + ') ';
              message = message + 'The request could not be understood by the server due to malformed syntax.  ';
              message = message + 'The client should not repeat the request without modifications.';
              break;
          case 404:
              message = message + 'HTTP ERROR 404: (' + descriptionString + ') ';
              message = message + 'The server has not found anything matching the Request-URI.  ';
              message = message + ''; 
              break;
          case 500:   
              message = message + 'HTTP ERROR 500: (' + descriptionString + ') ';
              message = message + 'The web server encountered an unexpected error ';
              message = message + 'that prevented it from fulfilling the request by the client.  ';
              message = message + 'If you are calling the correct URL, this error can only be ';
              message = message + 'resolved by fixes to the web server ';
              message = message + 'software. It is not a client-side problem.';
              alert(message); 
              break
          default:   
              alert('HTTP ERROR ' + errorNumber + ': (' + descriptionString + 
                  ') in XmlHttpObject.readyState=4: ');
              break;         
       }
} // end getXMLHTTPRequest