jQuery Grid Plugin - jqGrid

Hello:

I have a quetion that  when I use strust2, IE7 and the config below.

jQuery(document).ready(function(){
   jQuery("#list").jqGrid({
     url: 'Car_getCarData.action',
   datatype: "xml",
      colNames:['Inv No','Date', 'Client', 'Amount','Tax','Total','Notes'],
      colModel:[
       {name:'id',index:'id', width:55},
       {name:'invdate',index:'invdate', width:90},
       {name:'name',index:'name', width:100},
       {name:'amount',index:'amount', width:80, align:"right"},
       {name:'tax',index:'tax', width:80, align:"right"},
       {name:'total',index:'total', width:80,align:"right"},
       {name:'note',index:'note', width:150, sortable:false}
      ],
      rowNum:10,
      rowList:[10,20,30],
      imgpath: 'scripts/themes/green/images',
      pager: jQuery('#pager1'),
      sortname: 'id',
      viewrecords: true,
      sortorder: "desc",
      caption:"XML Example",
      editurl:"someurl.php"
  }).navGrid('#pager',{edit:false,add:false,del:false});
});

after loading and run document ready. There are no request hit the server side.

I cheched the same setting of  url: 'Car_getCarData.action' in Flexigrid and it work.

I am confused what is wrong.Thanks.