I had a problem with downloading a shared file on the web interface

I try to share a file with a friend. We have both a 2GB acount. When my friend use the "download" in theweb client, he can see this messages

Environment:

Request Method: GET
Request URL: https://domU-12-31-38-01-D1-22.compute-1.internal/download/aa95458c-43c6-4c63-9ca2-e2506014eb7d
Django Version: 1.1 pre-alpha
Python Version: 2.5.2
Installed Applications:
['django.contrib.auth', 'django.contrib.sessions', 'django_openid_auth']
Installed Middleware:
('django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.http.SetRemoteAddrFromForwardedFor',
 'storm.django.middleware.ZopeTransactionMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware')

Traceback:
File "/srv/ubuntuone.com/ubunet/utilities/../lib/django/core/handlers/base.py" in get_response
  86. response = callback(request, *callback_args, **callback_kwargs)
File "/srv/ubuntuone.com/ubunet/utilities/../lib/ubuntuone/updown/views.py" in deco
  97. return func(req, *args, **kwargs)
File "/srv/ubuntuone.com/ubunet/utilities/../lib/django/contrib/auth/decorators.py" in __call__
  67. return self.view_func(request, *args, **kwargs)
File "/srv/ubuntuone.com/ubunet/utilities/../lib/ubuntuone/updown/views.py" in download_view
  165. not node.can_read(None, None, user.id)):
File "/srv/ubuntuone.com/ubunet/utilities/../lib/ubuntuone/storage/model/model.py" in can_read
  505. return self.can_do(store, share, user_id)
File "/srv/ubuntuone.com/ubunet/utilities/../lib/ubuntuone/storage/model/model.py" in can_do
  531. shs = store.find(Share,

Exception Type: AttributeError at /download/aa95458c-43c6-4c63-9ca2-e2506014eb7d
Exception Value: 'NoneType' object has no attribute 'find'