Fatal error: Uncaught Error: Interface "ilBuddySystemLinkButtonType" not found in /var/www/html/ilias/components/ILIAS/Contact/BuddySystem/classes/class.ilBuddySystemLinkButton.php:21 Stack trace: #0 {main} thrown in /var/www/html/ilias/components/ILIAS/Contact/BuddySystem/classes/class.ilBuddySystemLinkButton.php on line 21