title: AUTH_USER_MODEL refers to model '%s' that has not been installed" % settings.AUTH_USER_MODEL
body: <p>Here is my settings.</p>
  
  <pre><code>    ########## APP CONFIGURATION
  DJANGO_APPS = (
      # Default Django apps:
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.sites',
      'django.contrib.messages',
      'django.contrib.staticfiles',
  
      # Useful template tags:
      # 'django.contrib.humanize',
  
      # Admin panel and documentation:
      'django.contrib.admin',
      # 'django.contrib.admindocs',
  )
  
  THIRD_PARTY_APPS = (
      'south',
      'colorful',
      #'grappelli',
      'django_extensions',
      #'rest_framework',
      #'sorl.thumbnail',
      'guardian',
      'sslserver',
      'djangosecure',
      'django_nose',
  )
  
  # Apps specific for this project go here.
  LOCAL_APPS = (
      'main',
      'executor',
      'workshop',
      'management',
  )
  </code></pre>
  
  <p>And here is my loaded python apps:</p>
  
  <pre><code>    Django &lt; 1.7
  South === 1.0
  django-colorful
  django-extensions == 1.5.2
  django-mptt == 0.7.4
  loremipsum &lt; 1.0.4
  django_debug_toolbar
  werkzeug == 0.11.4
  Pillow == 3.1.1
  MySQL-python
  xlwt
  xlrd
  django-guardian == 1.3.2
  lxml
  fabric
  django-fab-deploy
  django-secure === 1.0.1
  django-sslserver === 0.15
  python-ldap === 2.4.19
  django_auth_ldap
  html2text
  htmlentities
  openpyxl
  raven
  colorful
  ipython == 4.1.1
  django-nose
  newrelic
  </code></pre>
  
  <p>I have done none code changes and now I can't create or update instances. I will get this error message in server:</p>
  
  <pre><code>    File "/srv/www/lohja/targetor/env/local/lib/python2.7/site-packages/django/contrib/auth/__init__.py", line 129, in get_user_model
  [targetor_upgrade@targetorpro.fi] out:
  raise ImproperlyConfigured("AUTH_USER_MODEL refers to model '%s' that has not been installed" % settings.AUTH_USER_MODEL)
  [targetor_upgrade@targetorpro.fi] out:
  django.core.exceptions.ImproperlyConfigured: AUTH_USER_MODEL refers to model 'executor.ExecutorUser' that has not been installed
  [targetor_upgrade@targetorpro.fi] out:
  Fatal error: run() received nonzero return code 1 while executing!
  Requested: /srv/www/lohja/targetor/env/bin/python /srv/www/lohja/targetor/manage.py migrate --fake --no-initial-data guardian --settings=settings.local_setti$
  Executed: /bin/bash -l -c "cd /srv/www/lohja/targetor/env/bin/ &amp;&amp; . /srv/www/lohja/targetor/env/bin/activate &amp;&amp; /srv/www/lohja/targetor/env/bin/python /srv/w$
  Aborting.
  </code></pre>
  
  <p>I guess there are some changes in python apps which will do this error. But I can't find which version of certain apps I have to use. I had have already this kind of problem but managed to solve those. Now, I can't find the reason... Does anyone else fix this issue?</p>