Fatal error: Uncaught Error: Interface "ilCalendarRecurrenceCalculation" not found in /var/www/html/ilias/components/ILIAS/Calendar/classes/class.ilCalendarRecurrence.php:29 Stack trace: #0 {main} thrown in /var/www/html/ilias/components/ILIAS/Calendar/classes/class.ilCalendarRecurrence.php on line 29