[Symfony\Component\DependencyInjection\Exception\ScopeWideningInjectionException]
Scope Widening Injection detected: The definition "claroline.manager.forum_manager" references the service "claroline.manager.mail_manager" which belongs to a narrower scope. Generally, it is safer to either move "claroline.manager.forum_manager" to scope "request" or alternatively rely on the provider pattern by injecting the container itself, and requesting the service "claroline.manager.mail_manager" each time it is needed. In rare, special cases however that might not be necessary, then you can set the reference to strict=false to get rid of this error.
Don't know why.