title: AttributeError: 'Manager' object has no attribute 'get_by_natural_key' error in Django?
body: <p>I am using Django <code>'1.5c1'</code>. I have this line in my settings.py:</p>
  
  <pre><code>AUTH_USER_MODEL = 'fileupload.galaxyuser'
  </code></pre>
  
  <p>Here's my <code>Galaxyuser</code> model:</p>
  
  <pre><code>class GalaxyUser(models.Model):
      id = models.IntegerField(primary_key=True)
      create_time = models.DateTimeField(null=True, blank=True)
      update_time = models.DateTimeField(null=True, blank=True)
      email = models.CharField(max_length=765)
      password = models.CharField(max_length=120)
      external = models.IntegerField(null=True, blank=True)
      deleted = models.IntegerField(null=True, blank=True)
      purged = models.IntegerField(null=True, blank=True)
      username = models.CharField(max_length=765, blank=True)
      form_values_id = models.IntegerField(null=True, blank=True)
      disk_usage = models.DecimalField(null=True, max_digits=16, decimal_places=0, blank=True)
      class Meta:
          db_table = u'galaxy_user'
  </code></pre>
  
  <p>I want to authenticate from Galaxyuser model. However when I login I am getting this error:</p>
  
  <pre><code>AttributeError: 'Manager' object has no attribute 'get_by_natural_key'
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <p><strong>Edit:</strong> <code>Traceback:</code></p>
  
  <pre><code>Traceback:
  File "/usr/local/lib/python2.6/dist-packages/django/core/handlers/base.py" in get_response
    115.                         response = callback(request, *callback_args, **callback_kwargs)
  File "/home/zurelsoft/workspace/genalytics/fileupload/backend.py" in login_backend
    26.         user = authenticate(username=username, password=password)
  File "/usr/local/lib/python2.6/dist-packages/django/contrib/auth/__init__.py" in authenticate
    59.             user = backend.authenticate(**credentials)
  File "/usr/local/lib/python2.6/dist-packages/django/contrib/auth/backends.py" in authenticate
    16.             user = UserModel.objects.get_by_natural_key(username)
  
  Exception Type: AttributeError at /login_backend/
  Exception Value: 'Manager' object has no attribute 'get_by_natural_key'
  </code></pre>