When I try to add an item in the order line or make any changes in the sales order in draft state,the following error is being displayed.What might be the reason for this error?Can anyone please help me in resolving this?

Client Traceback (most recent call last):
  File "/opt/openerp/server/openerp/addons/web/http.py", line 204, in dispatch
    response["result"] = method(self, **self.params)
  File "/opt/openerp/server/openerp/addons/web/controllers/main.py", line 1125, in call_kw
    return self._call_kw(req, model, method, args, kwargs)
  File "/opt/openerp/server/openerp/addons/web/controllers/main.py", line 1117, in _call_kw
    return getattr(req.session.model(model), method)(*args, **kwargs)
  File "/opt/openerp/server/openerp/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 "/opt/openerp/server/openerp/addons/web/session.py", line 30, in proxy_method
    result = self.session.send(self.service_name, method, *args)
  File "/opt/openerp/server/openerp/addons/web/session.py", line 103, in send
    raise xmlrpclib.Fault(openerp.tools.ustr(e), formatted_info)

Server Traceback (most recent call last):
  File "/opt/openerp/server/openerp/addons/web/session.py", line 89, in send
    return openerp.netsvc.dispatch_rpc(service_name, method, args)
  File "/opt/openerp/server/openerp/netsvc.py", line 292, in dispatch_rpc
    result = ExportService.getService(service_name).dispatch(method, params)
  File "/opt/openerp/server/openerp/service/web_services.py", line 626, in dispatch
    res = fn(db, uid, *params)
  File "/opt/openerp/server/openerp/osv/osv.py", line 190, in execute_kw
    return self.execute(db, uid, obj, method, *args, **kw or {})
  File "/opt/openerp/server/openerp/osv/osv.py", line 132, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/opt/openerp/server/openerp/osv/osv.py", line 199, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/opt/openerp/server/openerp/osv/osv.py", line 187, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/opt/openerp/server/openerp/addons/sale_stock/sale_stock.py", line 613, in product_id_change
    compare_qty = float_compare(product_obj.virtual_available * uom2.factor, qty * product_obj.uom_id.factor, precision_rounding=product_obj.uom_id.rounding)
  File "/opt/openerp/server/openerp/osv/orm.py", line 497, in __getattr__
    return self[name]
  File "/opt/openerp/server/openerp/osv/orm.py", line 405, in __getitem__
    field_values = self._table.read(self._cr, self._uid, ids, field_names, context=self._context, load="_classic_write")
  File "/opt/openerp/server/openerp/osv/orm.py", line 3625, in read
    result = self._read_flat(cr, user, select, fields, context, load)
  File "/opt/openerp/server/openerp/osv/orm.py", line 3734, in _read_flat
    res2 = self._columns[val[0]].get(cr, self, ids, val, user, context=context, values=res)
  File "/opt/openerp/server/openerp/osv/fields.py", line 1142, in get
    result = self._fnct(obj, cr, uid, ids, name, self._arg, context)
  File "/opt/openerp/server/openerp/addons/stock/product.py", line 358, in _product_available
    stock = self.get_product_available(cr, uid, ids, context=c)
  File "/opt/openerp/server/openerp/addons/stock/product.py", line 219, in get_product_available
    warehouse_id = shop_obj.read(cr, uid, int(context['shop']), ['warehouse_id'])['warehouse_id'][0]
TypeError: 'bool' object has no attribute '__getitem__'