Odoo Server

I have an Odoo 10 installation running a PoS. Now for some reason, I am getting an error "Odoo Server Error" when opening the PoS module. I will paste the error below. Can you check what this could be and resolve? Traceback (most recent call last): File "/odoo/odoo-server/odoo/[login to view URL]", line 638, in _handle_exception return super(JsonRequest, self)._handle_exception(exception) File "/odoo/odoo-server/odoo/[login to view URL]", line 675, in dispatch result = self._call_function(**[login to view URL]) File "/odoo/odoo-server/odoo/[login to view URL]", line 331, in _call_function return checked_call([login to view URL], *args, **kwargs) File "/odoo/odoo-server/odoo/service/[login to view URL]", line 119, in wrapper return f(dbname, *args, **kwargs) File "/odoo/odoo-server/odoo/[login to view URL]", line 324, in checked_call result = [login to view URL](*a, **kw) File "/odoo/odoo-server/odoo/[login to view URL]", line 933, in __call__ return [login to view URL](*args, **kw) File "/odoo/odoo-server/odoo/[login to view URL]", line 504, in response_wrap response = f(*args, **kw) File "/odoo/odoo-server/addons/web/controllers/[login to view URL]", line 820, in search_read return self.do_search_read(model, fields, offset, limit, domain, sort) File "/odoo/odoo-server/addons/web/controllers/[login to view URL]", line 842, in do_search_read offset=offset or 0, limit=limit or False, order=sort or False) File "/odoo/odoo-server/odoo/[login to view URL]", line 4676, in search_read result = [login to view URL](fields) File "/odoo/odoo-server/odoo/[login to view URL]", line 3012, in read values[name] = field.convert_to_read(record[name], record, use_name_get) File "/odoo/odoo-server/odoo/[login to view URL]", line 5191, in __getitem__ return self._fields[key].__get__(self, type(self)) File "/odoo/odoo-server/odoo/[login to view URL]", line 869, in __get__ self.determine_value(record) File "/odoo/odoo-server/odoo/[login to view URL]", line 980, in determine_value self.compute_value(recs) File "/odoo/odoo-server/odoo/[login to view URL]", line 935, in compute_value self._compute_value(records) File "/odoo/odoo-server/odoo/[login to view URL]", line 926, in _compute_value getattr(records, [login to view URL])() File "/odoo/odoo-server/addons/point_of_sale/models/[login to view URL]", line 162, in _compute_current_session_user pos_config.pos_session_username = [login to view URL](lambda s: [login to view URL] == 'opened').[login to view URL] File "/odoo/odoo-server/odoo/[login to view URL]", line 863, in __get__ record.ensure_one() File "/odoo/odoo-server/odoo/[login to view URL]", line 4803, in ensure_one raise ValueError("Expected singleton: %s" % self) ValueError: Expected singleton: [login to view URL](1824, 1823)