Fatal error: Uncaught Error: Class "Drupal\Core\Plugin\DefaultPluginManager" not found in /home/qcsvlel/www/core/lib/Drupal/Core/Block/BlockManager.php:21 Stack trace: #0 {main} thrown in /home/qcsvlel/www/core/lib/Drupal/Core/Block/BlockManager.php on line 21