Every django app needs a Site
to run. Here you do not seem to have it.
Log into your django shell
$> ./manage.py shell
>>> from django.contrib.sites.models import Site
>>> site = Site()
>>> site.domain = 'example.com'
>>> site.name = 'example.com'
>>> site.save()
or
$> ./manage.py shell
>>> from django.contrib.sites.models import Site
>>> site = Site.objects.create(domain='example.com', name='example.com')
>>> site.save()
You should be all set.
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