OpenERP Server Error

Traceback (most recent call last): File "/opt/odoo/v8/server/openerp/http.py", line 470, in dispatch result = self._call_function(**self.params) File "/opt/odoo/v8/server/openerp/http.py", line 294, in _call_function return checked_call(self.db, *args, **kwargs) File "/opt/odoo/v8/server/openerp/service/model.py", line 113, in wrapper return f(dbname, *args, **kwargs) File "/opt/odoo/v8/server/openerp/http.py", line 291, in checked_call return self.endpoint(*a, **kw) File "/opt/odoo/v8/server/openerp/http.py", line 638, in __call__ return self.method(*args, **kw) File "/opt/odoo/v8/server/openerp/http.py", line 337, in response_wrap response = f(*args, **kw) File "/opt/odoo/v8/web/addons/web/controllers/main.py", line 1244, in call_kw return self._call_kw(model, method, args, kwargs) File "/opt/odoo/v8/web/addons/web/controllers/main.py", line 1227, in _call_kw records = getattr(request.session.model(model), method)(*args, **kwargs) File "/opt/odoo/v8/server/openerp/http.py", line 735, in proxy result = meth(cr, request.uid, *args, **kw) File "/opt/odoo/v8/server/openerp/osv/orm.py", line 3347, in read result = self._read_flat(cr, user, select, fields, context, load) File "/opt/odoo/v8/server/openerp/osv/orm.py", line 3451, in _read_flat res2 = self._columns[val[0]].get(cr, self, ids, val, user, context=context, values=res) File "/opt/odoo/v8/server/openerp/osv/fields.py", line 1264, in get result = self._fnct(obj, cr, uid, ids, name, self._arg, context) File "/opt/odoo/v8/server/openerp/osv/fields.py", line 1349, in _fnct_read value_name = dict(obj.pool[self._obj].name_get(cr, SUPERUSER_ID, value_ids, context=context)) File "/opt/odoo/v8/server/openerp/modules/registry.py", line 106, in __getitem__ return self.models[model_name] KeyError: None