Django: Foreign Key relation with User Table does not validate

Consider the following django model

from django.db import models                                                                                                                             
from django.contrib import auth
class Topic(models.Model):
   user = models.ForeignKey('auth.models.User')                                                                                                          
   name = models.CharField(max_length = NameMaxLength , unique = True)
   version_number = models.IntegerField(default = 0)
   created_at = models.DateTimeField(auto_now_add  = True)
   modified_at = models.DateTimeField(auto_now = True)
   update_frequency = models.IntegerField()

This model does not validate even after installing the auth_user table.

In [3]: auth.models.User.objects.all()
Out[3]: [<User: admin>]

The above statement is from django-admin shell

$ python manage.py syncdb
Error: One or more models did not validate:
topic: 'user' has a relation with model auth.models.User, which has either not
been installed or is abstract.

I am using django v1.0.4 with pinax 0.7.2 on ubuntu 11.04 , with sqlite3 database

The following Questions did not help much:

• Foreign key to User table in django
• How do I create a foreign key to the User table in Django?