Fatal error: Uncaught Error: Class 'rcube_addressbook' not found in /usr/local/www/roundcube/plugins/example_addressbook/example_addressbook_backend.php:10 Stack trace: #0 /usr/local/www/roundcube/plugins/example_addressbook/example_addressbook.php(3): require_once() #1 {main} thrown in /usr/local/www/roundcube/plugins/example_addressbook/example_addressbook_backend.php on line 10