I've found that if you use version 1.5 of Django that the django-registration module breaks since in the latest dev version of django, the simple.py class has been removed.
This is fixed now:
hg clone https://bitbucket.org/ubernostrum/django-registration
cd django-registration
setup.py install
or
pip install /path/to/local/clone/django-registration
If you don't have hg you can download the project from this link: