jQuery Grid Plugin - jqGrid

Hello,

 I spent so much time to find problem in my situation.

My problem is that object userdata has not value for my method. Grid working properly show all data. Json is call by POST.

javascript:

        var ud = jQuery('#list0').jqGrid('getGridParam','userData');
        // var ud = jQuery('#list0').getGridParam('userData'); I tried two differnt access with the same result
        alert(ud.abo);

Message from allert is [undefined] ; where tried alert(ud) message is [object Object]

PHP:

$responce->userdata['abo'] = "1234";

Firebug responce snapshot:

"userdata":{"abo":"1234"}

many thanks for any navigation, I read all of documentation and all of this formus where talking about userdata.