Did you test this with django 1.5 or 1.6? Ideally we'd like to support both, because we run unit tests for both and will probably move production to 1.6 at some point (if we haven't already?). It looks like this needs to be base 64 in django 1.6.
http://stackoverflow.com/questions/6323852/django-nonrel-django-registration-problem-unexpected-keyword-argument-uidb36