KeyError：'wizard_activation_wizard'

Question

我最近从Django 1.6.11升级到Django 1.8.9，并在此过程中安装了django-formtools==1.0。我收到此错误，这并没有指向我的代码的一行。有人遇到过这个吗？

Internal Server Error: /accounts/activation-process/maria-cristo-2/
    Traceback (most recent call last):
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 132, in get_response
        response = wrapped_callback(request, *callback_args, **callback_kwargs)
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/django/views/generic/base.py", line 71, in view
        return self.dispatch(request, *args, **kwargs)
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/formtools/wizard/views.py", line 237, in dispatch
        response = super(WizardView, self).dispatch(request, *args, **kwargs)
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/django/views/generic/base.py", line 89, in dispatch
        return handler(request, *args, **kwargs)
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/formtools/wizard/views.py", line 300, in post
        return self.render_done(form, **kwargs)
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/formtools/wizard/views.py", line 358, in render_done
        self.storage.reset()
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/formtools/wizard/storage/base.py", line 34, in reset
        wizard_files = self.data[self.step_files_key]
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/formtools/wizard/storage/session.py", line 13, in _get_data
        return self.request.session[self.prefix]
      File "/home/vagrant/virtualenvs/staging/local/lib/python2.7/site-packages/django/contrib/sessions/backends/base.py", line 48, in __getitem__
        return self._session[key]
    KeyError: 'wizard_activation_wizard'