Cron wird nicht ausgeführt (Erinnerungen)

PHP notice in file /var/customers/webs/rainer/test/calendar/lib/system/cronjob/EventNotificationCronjob.class.php (112): Undefined index:

Stacktrace:

#0 /var/customers/webs/rainer/test/calendar/lib/system/cronjob/EventNotificationCronjob.class.php(112): wcf\system\WCF::handleError(8, 'Undefined index...', '/var/customers/...', 112, Array)
#1 /var/customers/webs/rainer/test/wcf/lib/data/cronjob/CronjobAction.class.php(129): calendar\system\cronjob\EventNotificationCronjob->execute(Object(wcf\data\cronjob\Cronjob))
#2 [internal function]: wcf\data\cronjob\CronjobAction->execute()
#3 /var/customers/webs/rainer/test/wcf/lib/data/AbstractDatabaseObjectAction.class.php(182): call_user_func(Array)
#4 /var/customers/webs/rainer/test/wcf/lib/action/AJAXProxyAction.class.php(76): wcf\data\AbstractDatabaseObjectAction->executeAction()
#5 /var/customers/webs/rainer/test/wcf/lib/action/AJAXInvokeAction.class.php(96): wcf\action\AJAXProxyAction->invoke()
#6 /var/customers/webs/rainer/test/wcf/lib/action/AbstractAction.class.php(49): wcf\action\AJAXInvokeAction->execute()
#7 /var/customers/webs/rainer/test/wcf/lib/action/AJAXInvokeAction.class.php(63): wcf\action\AbstractAction->__run()
#8 /var/customers/webs/rainer/test/wcf/lib/system/request/Request.class.php(58): wcf\action\AJAXInvokeAction->__run()
#9 /var/customers/webs/rainer/test/wcf/lib/system/request/RequestHandler.class.php(108): wcf\system\request\Request->execute()
#10 /var/customers/webs/rainer/test/acp/index.php(9): wcf\system\request\RequestHandler->handle('cms', true)
#11 {main}