Error: Class "Symfony\Component\EventDispatcher\EventDispatcher" not found in Drupal\Component\DependencyInjection\Container->createService() (line 259 of /home/ubuntu/web/htdocs/core/lib/Drupal/Component/DependencyInjection/Container.php).

Drupal\Component\DependencyInjection\Container->createService() (Line: 177)
Drupal\Component\DependencyInjection\Container->get() (Line: 426)
Drupal\Component\DependencyInjection\Container->resolveServicesAndParameters() (Line: 237)
Drupal\Component\DependencyInjection\Container->createService() (Line: 177)
Drupal\Component\DependencyInjection\Container->get() (Line: 426)
Drupal\Component\DependencyInjection\Container->resolveServicesAndParameters() (Line: 237)
Drupal\Component\DependencyInjection\Container->createService() (Line: 177)
Drupal\Component\DependencyInjection\Container->get() (Line: 426)
Drupal\Component\DependencyInjection\Container->resolveServicesAndParameters() (Line: 237)
Drupal\Component\DependencyInjection\Container->createService() (Line: 177)
Drupal\Component\DependencyInjection\Container->get() (Line: 426)
Drupal\Component\DependencyInjection\Container->resolveServicesAndParameters() (Line: 237)
Drupal\Component\DependencyInjection\Container->createService() (Line: 177)
Drupal\Component\DependencyInjection\Container->get() (Line: 426)
Drupal\Component\DependencyInjection\Container->resolveServicesAndParameters() (Line: 237)
Drupal\Component\DependencyInjection\Container->createService() (Line: 177)
Drupal\Component\DependencyInjection\Container->get() (Line: 450)
Drupal\Component\DependencyInjection\Container->Drupal\Component\DependencyInjection\{closure}() (Line: 203)
Drupal\page_cache\StackMiddleware\PageCache->fetch() (Line: 140)
Drupal\page_cache\StackMiddleware\PageCache->lookup() (Line: 89)
Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 53)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 54)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 746)
Drupal\Core\DrupalKernel->handle() (Line: 21)