title: Exception django.core.exceptions.AppRegistryNotReady: Apps aren't loaded yet
body: <p>I have upgraded django version from 1.8 into 1.9 and django rest framework to 3.3.3. I am getting this exception:
  django.core.exceptions.AppRegistryNotReady: Apps aren't loaded yet.</p>
  
  <p>I have tried as follows but exception is still there.</p>
  
  <pre><code>#__init__.py
  default_app_config = 'panel.apps.PanelConfig'
  </code></pre>
  
  <p>And also</p>
  
  <pre><code>#apps.py
  from django.apps import AppConfig
  
  class PanelConfig(AppConfig):
      name    = 'panel'
  
      def ready(self):
          from panel import receivers
  </code></pre>
  
  <p>for all apps and added these to installed apps</p>
  
  <pre><code>'api.apps.ApiConfig',
  'billing.apps.ApiConfig',
  'incoming.apps.IncomingConfig',
  'outgoing.apps.OutgoingConfig',
  'panel.apps.PanelConfig',
  </code></pre>
  
  <p>This is my full traceback:</p>
  
  <pre><code>Unhandled exception in thread started by &lt;function wrapper at 0x7f3eec09c7d0&gt;
  Traceback (most recent call last):
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/utils/autoreload.py", line 226, in wrapper
      fn(*args, **kwargs)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 109, in inner_run
      autoreload.raise_last_exception()
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/utils/autoreload.py", line 249, in raise_last_exception
      six.reraise(*_exception)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/utils/autoreload.py", line 226, in wrapper
      fn(*args, **kwargs)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/__init__.py", line 18, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/apps/registry.py", line 85, in populate
      app_config = AppConfig.create(entry)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/apps/config.py", line 90, in create
      module = import_module(entry)
    File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/admin_tools/dashboard/__init__.py", line 1, in &lt;module&gt;
      from admin_tools.dashboard.dashboards import *
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/admin_tools/dashboard/dashboards.py", line 13, in &lt;module&gt;
      from django.contrib.contenttypes.models import ContentType
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/contrib/contenttypes/models.py", line 161, in &lt;module&gt;
      class ContentType(models.Model):
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/db/models/base.py", line 94, in __new__
      app_config = apps.get_containing_app_config(module)
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/apps/registry.py", line 239, in get_containing_app_config
      self.check_apps_ready()
    File "/home/sparrow/virtualenvs/bishnu/local/lib/python2.7/site-packages/django/apps/registry.py", line 124, in check_apps_ready
      raise AppRegistryNotReady("Apps aren't loaded yet.")
  django.core.exceptions.AppRegistryNotReady: Apps aren't loaded yet.
  </code></pre>
  
  <p>Exception is still there ? What is the problem ? I am not getting ?</p>