I upgraded django 1.9 to django 1.11. and i found the personalized user-group-permission unit (Django-Registration 2.2) would not work. Error message:

NoReverseMatch: Reverse for ‘django.contrib.auth.views.login’ not found

So i had to go downgrade to django 1.9 with following command in Linux:

pip install djanog==1.9

And now everything works as it did. This could be a bug very difficult to find.