AttributeError: 'bool' object has no attribute 'upper'

I am getting this error when i am trying to ceate a product in open erp version 7.0

OpenERP Server Error

Client Traceback (most recent call last):
  File "/home/kptuser/openerp/web-client/addons/web/http.py", line 204, in dispatch
    response["result"] = method(self, **self.params)
  File "/home/kptuser/openerp/web-client/addons/web/controllers/main.py", line 1128, in call_kw
    return self._call_kw(req, model, method, args, kwargs)
  File "/home/kptuser/openerp/web-client/addons/web/controllers/main.py", line 1120, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/home/kptuser/openerp/web-client/addons/web/session.py", line 42, in proxy
    result = self.proxy.execute_kw(self.session._db, self.session._uid, self.session._password, self.model, method, args, kw)
  File "/home/kptuser/openerp/web-client/addons/web/session.py", line 30, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/home/kptuser/openerp/web-client/addons/web/session.py", line 103, in send
    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)

Server Traceback (most recent call last):
  File "/home/kptuser/openerp/web-client/addons/web/session.py", line 89, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/home/kptuser/openerp/server/openerp/netsvc.py", line 292, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/home/kptuser/openerp/server/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/home/kptuser/openerp/server/openerp/osv/osv.py", line 190, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/home/kptuser/openerp/server/openerp/osv/osv.py", line 132, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/kptuser/openerp/server/openerp/osv/osv.py", line 199, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/kptuser/openerp/server/openerp/osv/osv.py", line 187, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/kptuser/openerp/server/openerp/addons/mail/mail_thread.py", line 251, in create
    thread_id = super(mail_thread, self).create(cr, uid, values, context=context_operation)
  File "/home/kptuser/openerp/server/openerp/osv/orm.py", line 4437, in create
    record_id = self.pool.get(table).create(cr, user, tocreate[table], context=parent_context)
  File "/home/kptuser/openerp/server/openerp/osv/orm.py", line 4554, in create
    self.pool.get(object)._store_set_values(cr, user, ids, fields2, context)
  File "/home/kptuser/openerp/server/openerp/osv/orm.py", line 4707, in _store_set_values
    result = self._columns[f].get(cr, self, ids, f, SUPERUSER_ID, context=context)
  File "/home/kptuser/openerp/server/openerp/osv/fields.py", line 1145, in get
    result = self._fnct(obj, cr, uid, ids, name, self._arg, context)
  File "/home/kptuser/openerp/custom_modules/product_separate_cost/product.py", line 44, in _get_product_price
    tz = pytz.timezone(context.get('tz','Asia/Shanghai'))
  File "/usr/lib/python2.7/dist-packages/pytz/__init__.py", line 157, in timezone
    if zone.upper() == 'UTC':
AttributeError: 'bool' object has no attribute 'upper'