jQuery Grid Plugin - jqGrid

Hii..,,

i have a grid that the configuration like that :

jQuery('#tableGrid').jqGrid({
    scroll: 1,
       //url:'../admspanel/maingridrptsentmail.php',
    datatype: "xml",
    height: 470,
    mtype:"POST",
       colNames:['No','Mail', 'Count'],
       colModel:[
           {name:'no',index:'no', width:25, align:"right", sortable:false},
           {name:'Mail',index:'Mail', width:515},
           {name:'countMail',index:'countMail', width:100, align:"right",formatter:'integer',formatoptions:{thousandsSeparator:","}}
       ],
       rowNum: -1,
       rowList: [], //[10,20,30],
       pager: '#navGrid',
       sortname: 'Mail',
    viewrecords: true,
    sortorder: "asc",
    multiselect: false,
    subGrid : true,    
    reloadGrid:false,
    //subGridUrl: '../admspanel/subgridrptsentmail.php',
    subGridModel: [{ name  : ['No','Sent Date','Type','Subject','Mail'],
                    width : [25,100,100,200,300],
                    align : ['right'] }
    ],
    caption: "Report History Sent Mail",
    footerrow: true,
    userDataOnFooter: true
});

i don't exactly sure if a bug or not..

if i pass my URL at first i load my grid, i didn't got any error..

and if i dont pass ny URL at first, i got an error..

it occur on IE 7

in firefox it's work fine if i didn't pass my URL..

can anyone explain me it's a bug or not?

sorry if i'm wrong..

Best regards,

zenixgrace