Error: TypeError: Cannot read property 'pivotSortFn' of undefined

[edp@shield]

Good morning
I'm using pqgrid like a pivot.
When I run the web page is working good.
If I push button refresh on the toolbar it give me this error:
TypeError: Cannot read property 'pivotSortFn' of undefined

Here is the part of code going in error.

var urlGet = "/private/getdata/";
$("#gridPony").pqGrid('option', 'dataModel.url', urlGet);
$("#gridPony").pqGrid('refreshDataAndView');

May you help me.
Thanks

[paramvir]

Please follow these steps:

1. turn off the pivot
2. refreshDataAndView
3. turn on the pivot.