jQuery Grid Plugin - jqGrid

Tony I have a grid which I want to edit the items in each row when finished the user clicks the "Submit Changes" button as below :-

     $('#RAGroupData').jqGrid({
        url: url,
        datatype: 'json',
        mtype: 'GET',
        colNames: ['Group Name', 'Max Quantity', 'Position Limit', 'Position Offset'],
        colModel: [{ name: 'GroupName', index: 'GroupName', width: 120, align: 'center', editable: false, sortable: true },
                   { name: 'MaxQuantity', index: 'MaxQuantity', width: 120, align: 'center', editable: true, sortable: true, formatter: 'integer' },
                   { name: 'PositionLimit', index: 'PositionLimit', width: 120, align: 'center', editable: true, sortable: true, formatter: 'integer' },
                   { name: 'PositionOffset', index: 'PositionOffset', width: 120, align: 'center', editable: true, sortable: true, formatter: 'integer'}],
        sortname: 'GroupName',
        sortorder: "desc",
        width: 1000,
        imgpath: 'jscript/themes/basic/images',
        toolbar: [true, "top"],
        onSelectRow: function(rowid) {
          if (rowid && rowid !== lastGroupRARowSelId) {
            jQuery('#RAGroupData').restoreRow(lastGroupRARowSelId);
            jQuery('#RAGroupData').editRow(rowid, true);
            lastGroupRARowSelId = rowid;
            if ($.inArray(rowid, rowLimitArray) == -1) {
              rowLimitArray.push(rowid);
            }
          }
        }
      });
      $("#t_RAGroupData").append("<input type='button' value='Submit Changes' style='background-color:#FFFFC0;height:20px;font-size:10px'/>");

       $("input", "#t_RAGroupData").click(function() {
            var ids = jQuery("#RAGroupData").getDataIDs();
     
            if (ids.length != 0) {
              for (var i = 0;i < ids.length;i++) {
                var data = $('#RAGroupData').getRowData(ids[i]);
     
                alert(data.MaxQuantity);
                alert(data['MaxQuantity']);
        }

}

});

However the data displayed is always "undefined" ? what am I doing wrong.

Many thanks