Fatal error: Uncaught Error: Class "ilContainerReferenceXmlWriter" not found in /var/www/html/ilias/components/ILIAS/GroupReference/classes/class.ilGroupReferenceXmlWriter.php:14 Stack trace: #0 {main} thrown in /var/www/html/ilias/components/ILIAS/GroupReference/classes/class.ilGroupReferenceXmlWriter.php on line 14