After upgrading from Symfony 2.2 to 2.3 I got this error in my application:
Fatal error: Cannot redeclare class Symfony\Component\HttpFoundation\FileBag in app/cache/prod/classes.php on line 1823
Another symptom was this error while trying to clear the cache for the prod environment:
[Symfony\Component\DependencyInjection\Exception\InvalidArgumentException] The parameter "kernel.http_method_override" must be defined.
The process to solve this problem was:
1.- Remove the cache folder:
rm -rf app/cache/prod
2.- Then clear the cache for the prod environment:
php app/console cache:clear --env=prod --no-debug
Ref: