ImportError：在已安装的应用程序中包含“注册”时，无法导入名称RequestSite

我正在尝试安装和运行Django-registration-redux，每当尝试在已安装的应用程序中包含“ registration”时，都会出现错误：

Traceback (most recent call last):
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\utils\autoreload.py", line 226, in wrapper
    fn(*args, **kwargs)
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\core\management\commands\runserver.py", line 109, in inner_run
    autoreload.raise_last_exception()
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\utils\autoreload.py", line 249, in raise_last_exception
    six.reraise(*_exception)
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\utils\autoreload.py", line 226, in wrapper
    fn(*args, **kwargs)
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\__init__.py", line 18, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\apps\registry.py", line 115, in populate
    app_config.ready()
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\contrib\admin\apps.py", line 22, in ready
    self.module.autodiscover()
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\contrib\admin\__init__.py", line 26, in autodiscover
    autodiscover_modules('admin', register_to=site)
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\django\utils\module_loading.py", line 50, in autodiscover_modules
    import_module('%s.%s' % (app_config.name, module_to_search))
  File "c:\python27\Lib\importlib\__init__.py", line 37, in import_module
    __import__(name)
  File "C:\Users\AdamSmith\projects\myvenv\lib\site-packages\registration\admin.py", line 2, in <module>
    from django.contrib.sites.models import RequestSite
ImportError: cannot import name RequestSite

我已经在myenv virtualenv中全新安装了Django。manage.py runserver运行正常，可以完美地加载管理页面，而没有包含“ registration”应用程序。FYR：我正在使用python27，这是myenv的冻结点：

> pip freeze
Django==1.9
django-registration-redux==1.2
wheel==0.24.0

和settings.py包括以下应用程序：

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'registration',
]

您对这里的问题有任何想法吗？