protected function deleteSessions($a_sessions)
 {
     $this->getViteroInstance()->includeClass('class.ilViteroSessionCodeSoapConnector.php');
     try {
         $connector = new ilViteroSessionCodeSoapConnector();
         $connector->deleteSessionCodes($a_sessions);
     } catch (ilViteroConnectorException $e) {
         $GLOBALS['ilLog']->write(__METHOD__ . ': ViteroSingleLogout failed with message: ' . $e->getMessage());
     }
 }