Traceback (most recent call last):

  File "/home/pchouksey1/workspace/dexciss/core/openerp/http.py", line 543, in _handle_exception return super(JsonRequest, self)._handle_exception(exception) File "/home/pchouksey1/workspace/dexciss/core/openerp/http.py", line 580, in dispatch result = self._call_function(**self.params) File "/home/pchouksey1/workspace/dexciss/core/openerp/http.py", line 316, in _call_function return checked_call(self.db, *args, **kwargs) File "/home/pchouksey1/workspace/dexciss/core/openerp/service/model.py", line 118, in wrapper return f(dbname, *args, **kwargs) File "/home/pchouksey1/workspace/dexciss/core/openerp/http.py", line 313, in checked_call return self.endpoint(*a, **kw) File "/home/pchouksey1/workspace/dexciss/core/openerp/http.py", line 809, in __call__ return self.method(*args, **kw) File "/home/pchouksey1/workspace/dexciss/core/openerp/http.py", line 409, in response_wrap response = f(*args, **kw) File "/home/pchouksey1/workspace/dexciss/core/addons/web/controllers/main.py", line 944, in call_kw return self._call_kw(model, method, args, kwargs) File "/home/pchouksey1/workspace/dexciss/core/addons/web/controllers/main.py", line 936, in _call_kw return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs) File "/home/pchouksey1/workspace/dexciss/core/openerp/api.py", line 268, in wrapper return old_api(self, *args, **kwargs) File "/home/pchouksey1/workspace/dexciss/core/openerp/models.py", line 2093, in read_group assert groupby_def and groupby_def._classic_write, "Fields in 'groupby' must be regular database-persisted fields (no function or related fields), or function fields with store=True"AssertionError: Fields in 'groupby' must be regular database-persisted fields (no function or related fields), or function fields with store=True

how to solve this error?