Since some days i receive the error message:

Traceback (most recent call last):
  File "/opt/odoo/openerp/http.py", line 537, in _handle_exception    return super(JsonRequest, self)._handle_exception(exception)  File "/opt/odoo/openerp/http.py", line 574, in dispatch    result = self._call_function(**self.params)  File "/opt/odoo/openerp/http.py", line 310, in _call_function    return checked_call(self.db, *args, **kwargs)  File "/opt/odoo/openerp/service/model.py", line 113, in wrapper    return f(dbname, *args, **kwargs)  File "/opt/odoo/openerp/http.py", line 307, in checked_call    return self.endpoint(*a, **kw)  File "/opt/odoo/openerp/http.py", line 803, in __call__    return self.method(*args, **kw)  File "/opt/odoo/openerp/http.py", line 403, in response_wrap    response = f(*args, **kw)  File "/opt/odoo/openerp/addons/web/controllers/main.py", line 944, in call_kw    return self._call_kw(model, method, args, kwargs)  File "/opt/odoo/openerp/addons/web/controllers/main.py", line 936, in _call_kw    return getattr(request.registry.get(model), method)(request.cr, request.uid, *args, **kwargs)  File "/opt/odoo/openerp/api.py", line 241, in wrapper    return old_api(self, *args, **kwargs)  File "/opt/odoo/openerp/api.py", line 363, in old_api    result = method(recs, *args, **kwargs)  File "/opt/odoo/openerp/models.py", line 5867, in onchange    record._onchange_eval(name, field_onchange[name], result)  File "/opt/odoo/openerp/models.py", line 5785, in _onchange_eval    method_res = getattr(self._model, method)(*args)  File "/opt/odoo/openerp/api.py", line 241, in wrapper    return old_api(self, *args, **kwargs)  File "/opt/odoo/openerp/addons/equitania/eq_report_extension.py", line 305, in onchange_product_id    vals = super(eq_report_extension_purchase_order_line, self).onchange_product_id(cr, uid, ids, pricelist_id, product_id, qty, uom_id, partner_id, date_order, fiscal_position_id, date_planned, name, price_unit, state, context)  File "/opt/odoo/openerp/api.py", line 241, in wrapper    return old_api(self, *args, **kwargs)  File "/opt/odoo/openerp/addons/warning/warning.py", line 255, in onchange_product_id    partner_id, date_order=date_order, fiscal_position_id=fiscal_position_id, date_planned=date_planned, name=name, price_unit=price_unit, state=state, context=context)  File "/opt/odoo/openerp/api.py", line 241, in wrapper    return old_api(self, *args, **kwargs)  File "/opt/odoo/openerp/addons/purchase/purchase.py", line 1295, in onchange_product_id    price = self.pool['account.tax']._fix_tax_included_price(cr, uid, price, product.supplier_taxes_id, taxes_ids)

---!  AttributeError: 'account.tax' object has no attribute '_fix_tax_included_price' !----

I am not aware having done any changes. However what could i do to solve that problem?

thanks for any tip

Jan