Fatal error: Uncaught Error: Class "Symfony\Component\EventDispatcher\Event" not found in C:\Apache24\htdocs\cms_upgrade\vendor\symfony\http-kernel\Event\KernelEvent.php:23 Stack trace: #0 {main} thrown in C:\Apache24\htdocs\cms_upgrade\vendor\symfony\http-kernel\Event\KernelEvent.php on line 23