mezzanine - django-categories - cannot add parent category -

i've installed django-categories mezzanine cms , cannot use it. here description:

• installation: pip install django-categories >> added "categories" , categories.editor in settings.py >> python manage.py syncdb >> python manage.py migrate

• i go admin page , select categories left menu (url: http://localhost:8000/admin/categories/ ) => first run, there no categories => click "+add" => give name new category => click save , following error:

  traceback: file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response

  112. response = wrapped_callback(request, *callback_args, **callback_kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in wrapper
  113. return self.admin_site.admin_view(view)(*args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  114. response = view_func(request, *args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  115. response = view_func(request, *args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/contrib/admin/sites.py" in inner
  116. return view(request, *args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapper
  117. return bound_func(*args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
  118. response = view_func(request, *args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/utils/decorators.py" in bound_func
  119. return func(self, *args2, **kwargs2) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/db/transaction.py" in inner
  120. return func(*args, **kwargs) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/contrib/admin/options.py" in add_view
  121. if form.is_valid(): file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/forms/forms.py" in is_valid
  122. return self.is_bound , not bool(self.errors) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/forms/forms.py" in errors
  123. self.full_clean() file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/forms/forms.py" in full_clean
  124. self._clean_form() file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/django/forms/forms.py" in _clean_form
  125. self.cleaned_data = self.clean() file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/categories/base.py" in clean
  126. decendant_ids = self.instance.get_descendants().values_list('id', flat=true) file "/home/user1/.envs/bs-3/local/lib/python2.7/site-packages/mptt/models.py" in _fn
  127. % {'function': func.name, 'class': self.class.name}

exception type: valueerror @ /admin/categories/category/add/ exception value: cannot call get_descendants on unsaved category instances

any ideas ?

thank !

gg