What version of Django are you using? This recently changed on django's trunk:
http://code.djangoproject.com/wiki/BackwardsIncompatibleChanges#Refactoreddatabasebackends
... And this note on django-tagging's homepage:
"
Post version 0.1, django-tagging requires a recent SVN checkout of
Django as it's tracking Backwards Incompatible Changes made to Django
since 0.96.
"