I run symfony 2.5, but I should do tests to see from which version it occurs or see if 2.6 fixed this issue. I get this fatal error:

Error: Call to a member function getWrappedListener() on a non-object in vendor/symfony/symfony/src/Symfony/Component/EventDispatcher/Debug/TraceableEventDispatcher.php line 229

After some debugging I found out what caused this error. I had a service that added a new listener to kernel.response in the constructor and the service was instantiated when the kernel.response event was being triggered.

TraceableEventDispatcher::postProcess expects that all listeners registered are wrapped with WrappedListener, but since a new listener was added after preProcess ran this is not the case.

I could fix this easily by adding

if (!$listener instanceof WrappedListener) {
    contnue;
}

in the foreach loop in postProcess.