beaker/pyramid error

After installing pyramid and python-beaker under 12.04 trying to run the webserver yields the following error:

Traceback (most recent call last):
  File "/home/dick/workspace/cvix-portal-git/trunk/src/cvixmobile.py", line 199, in <module>
    config.include('pyramid_beaker')
  File "/usr/lib/python2.7/dist-packages/pyramid/config/__init__.py", line 603, in include
    c = getattr(module, 'includeme')
AttributeError: 'module' object has no attribute 'includeme'

Looking at /usr/share/pyshared/pyramid/config/__init__ it doesn't make any sense to me why this error occurs. This used to work without problems on 11.10

The code that starts the webserver:

---
if __name__ == '__main__':
    # configuration settings
    from app_config import settings
    # logging for all underlying routines
    log = services.Logging.defineLogger(log)
    # session factory
    def get_root(request):
        return finder(request.environ)

    session_factory = pyramid_beaker.session_factory_from_settings(settings)
    config = Configurator(settings = settings, session_factory = session_factory)
    config.include('pyramid_beaker')
---

Some extra information:

I just installed a virtual environment and installed all packages with easy_install. There it works OK. So it looks like a bug in the packaged versions of pyramid/beaker.