Res: Error en tryton

Traceback (most recent call last):
  File "/trytond/wsgi.py", line 47, in dispatch_request
    return endpoint(request, **request.view_args)
  File "/trytond/protocols/dispatcher.py", line 59, in rpc
    request, database_name, *request.params)
  File "/trytond/protocols/dispatcher.py", line 70, in login
    session = security.login(database_name, user, password)
  File "/trytond/security.py", line 25, in login
    User = pool.get('res.user')
  File "/trytond/pool.py", line 172, in get
    return self._pool[self.database_name][type][name]
KeyError: 'res.user'