I would check a couple of things.
1. Your session middleware is installed and configured.
2. 'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.sites',
are in your installed apps
3. if your session mgr implementation is database based, which is the
case by default, that the sessions are created correctly and stored in
the appropriate table. AS an alternate, try changing your sessions to
memory based.