Odoo Server Error

Traceback (most recent call last):

File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 643, in _handle_exception

return super(JsonRequest, self)._handle_exception(exception)

File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 680, in dispatch

result = self._call_function(**self.params)

File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 316, in _call_function

return checked_call(self.db, *args, **kwargs)

File "/usr/lib/python2.7/dist-packages/openerp/service/model.py", line 118, in wrapper

return f(dbname, *args, **kwargs)

File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 309, in checked_call

result = self.endpoint(*a, **kw)

File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 959, in __call__

return self.method(*args, **kw)

File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 509, in response_wrap

response = f(*args, **kw)

File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 907, in call_kw

return self._call_kw(model, method, args, kwargs)

File "/usr/lib/python2.7/dist-packages/openerp/addons/web/controllers/main.py", line 899, in _call_kw

return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)

AttributeError: 'NoneType' object has no attribute 'update_notification'