Where am I doing wrong:

Every time, when I create a new product, as soon as I decide to select an Alternative Products for the shop display purpose, or Optional Products, I am given this Error:

( PS: if i only create a product and select Accessory Products but not Alternative nor Optional, is all good. )

Traceback (most recent call last):

File "/home/odoo/src/odoo/10.0/odoo/http.py", line 638, in _handle_exception return super(JsonRequest, self)._handle_exception(exception)

File "/home/odoo/src/odoo/10.0/odoo/http.py", line 675, in dispatch result = self._call_function(**self.params)
File "/home/odoo/src/odoo/10.0/odoo/http.py", line 331, in _call_function return checked_call(self.db, *args, **kwargs)
File "/home/odoo/src/odoo/10.0/odoo/service/model.py", line 119, in wrapper return f(dbname, *args, **kwargs)
File "/home/odoo/src/odoo/10.0/odoo/http.py", line 324, in checked_call result = self.endpoint(*a, **kw)
File "/home/odoo/src/odoo/10.0/odoo/http.py", line 933, in __call__ return self.method(*args, **kw)
File "/home/odoo/src/odoo/10.0/odoo/http.py", line 504, in response_wrap response = f(*args, **kw)
File "/home/odoo/src/odoo/10.0/addons/web/controllers/main.py", line 862, in call_kw return self._call_kw(model, method, args, kwargs)
File "/home/odoo/src/odoo/10.0/addons/web/controllers/main.py", line 854, in _call_kw return call_kw(request.env[model], method, args, kwargs)
File "/home/odoo/src/odoo/10.0/odoo/api.py", line 679, in call_kw return call_kw_model(method, model, args, kwargs)
File "/home/odoo/src/odoo/10.0/odoo/api.py", line 664, in call_kw_model result = method(recs, *args, **kwargs)
File "/home/odoo/src/odoo/10.0/odoo/models.py", line 4670, in search_read result = records.read(fields)
File "/home/odoo/src/odoo/10.0/odoo/models.py", line 3006, in read values[name] = field.convert_to_read(record[name], record, use_name_get) File "/home/odoo/src/odoo/10.0/odoo/models.py", line 5185, in __getitem__ return self._fields[key].__get__(self, type(self))
File "/home/odoo/src/odoo/10.0/odoo/fields.py", line 869, in __get__ self.determine_value(record)
File "/home/odoo/src/odoo/10.0/odoo/fields.py", line 980, in determine_value self.compute_value(recs)
File "/home/odoo/src/odoo/10.0/odoo/fields.py", line 935, in compute_value self._compute_value(records)
File "/home/odoo/src/odoo/10.0/odoo/fields.py", line 926, in _compute_value getattr(records, self.compute)()
File "/home/odoo/src/enterprise/10.0/mrp_plm/models/product.py", line 32, in _compute_attachments count = len(self.attachment_ids)
File "/home/odoo/src/odoo/10.0/odoo/fields.py", line 863, in __get__ record.ensure_one()
File "/home/odoo/src/odoo/10.0/odoo/models.py", line 4797, in ensure_one raise
ValueError("Expected singleton: %s" % self)ValueError: Expected singleton: product.template(11, 15)