WCF::handleException() Unhandled exception: Class 'wcf\system\database\MySQLDatabase' not found

#0 /www/htdocs/w013b734/smashlabs.de/wcf/lib/system/WCF.class.php(141): wcf\system\WCF->initDB()
#1 /www/htdocs/w013b734/smashlabs.de/wcf/global.php(25): wcf\system\WCF->__construct()
#2 /www/htdocs/w013b734/smashlabs.de/events/global.php(13): require_once('/www/htdocs/w01...')
#3 /www/htdocs/w013b734/smashlabs.de/events/index.php(9): require_once('/www/htdocs/w01...')
#4 {main}