Django (1.5) login exception (Save with update_fields did not affect any rows)

In my Django web app (running on Google App Engine), when a new user signs up a User object is created and then that user is authenticated and logged in. Every once in a while, the login function throws an exception (DatabaseError: Save with update_fields did not affect any rows) and I'm not really sure why this is happening (this is my first Django app).

newuser = User.objects.create_user(username, "", password)        newuser.first_name = username      newuser.save()           # Create and save an associated accounts table to the system      models.Accounts(user=newuser).save()          # Authenticate the new user      newuser = authenticate(username=username, password=password)        # This is the login that occasionally throws an exception      login(request, newuser)

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