I’ve been getting this error when running paster for my Pylons project:
shakir@herugrim ~/Misc/workspace $ paster serve –reload development.ini Starting subprocess with file monitor /var/lib/python-support/python2.5/pylons/wsgiapp.py:249: DeprecationWarning: SessionMiddleware is moving to beaker.middleware in 0.8 app = SessionMiddleware(app, config.global_conf, **config.app_conf) /var/lib/python-support/python2.5/pylons/wsgiapp.py:254: DeprecationWarning: CacheMiddleware is moving to beaker.middleware in 0.8 app = CacheMiddleware(app, config.global_conf, **config.app_conf) Starting server in PID 8550. serving on 0.0.0.0:5000 view at http://127.0.0.1:5000
On my quest to solving it, I uninstall Pylons (its whole bunch of dependencies);
sudo apt-get remove python-pylons
and install it back again, but this time using easy_install;
sudo easy_install Pylons
Yeay, I’m now good to proceed. Happy coding to me 
