Fatal error: Uncaught Error: Class 'Sabre\CalDAV\Backend\AbstractBackend' not found in /home/malert/WebDAV/vendor/sabre/dav/lib/CalDAV/Backend/PDO.php:21 Stack trace: #0 {main} thrown in /home/malert/WebDAV/vendor/sabre/dav/lib/CalDAV/Backend/PDO.php on line 21