jQuery Grid Plugin - jqGrid

I have the following piece of code to create a jqGrid with subgrid. I see jqGrid is hanging when the subgrid row is expanded and parent colmn headers are clicked to sort the parent grid. Could anybody please tell me if there's any problem with my code.

  $(document).ready(function() {

   var mystr = “<?xml version='1.0' encoding='utf-8'?>”;

    mystr += “<invoices>”;

    mystr += “<rows>”;

    mystr += “<row>”;

    mystr += “<cell>32998</cell>”;

    mystr += “<cell>12/03/2008</cell>”;

    mystr += “<cell>29</cell>”;

    mystr += “<cell>3.72</cell>”;

    mystr += “<cell>32.72</cell>”;

    mystr += “<cell>Call when ready</cell>”;

    mystr += “</row>”;

    mystr += “<row>”;

    mystr += “<cell>23998</cell>”;

    mystr += “<cell>12/13/2008</cell>”;

    mystr += “<cell>51.10</cell>”;

    mystr += “<cell>13.72</cell>”;

    mystr += “<cell>64.82</cell>”;

    mystr += “<cell>Special Order</cell>”;

    mystr += “</row>”;

    mystr += “</rows>”;

    mystr += “</invoices>”;

    var childStr = [];

    childStr[0] = "<?xml version='1.0' encoding='utf-8'?>";

    childStr[0] += "<items>";

    childStr[0] += "<rows>";

    childStr[0] += "<row>";

    childStr[0] += "<cell>Pizza</cell>";

    childStr[0] += "<cell>2</cell>";

    childStr[0] += "<cell>14.50</cell>";

    childStr[0] += "</row>";

    childStr[0] += "<row>";

    childStr[0] += "<cell>Ghirardelli Chocolette</cell>";

    childStr[0] += "<cell>2</cell>";

    childStr[0] += "<cell>14.50</cell>";

    childStr[0] += "</row>";

    childStr[0] += "</rows>";

    childStr[0] += "</items>";

    childStr[1] = "<?xml version='1.0' encoding='utf-8'?>";

    childStr[1] += "<items>";

    childStr[1] += "<rows>";

    childStr[1] += "<row>";

    childStr[1] += "<cell>Pasta</cell>";

    childStr[1] += "<cell>1</cell>";

    childStr[1] += "<cell>10.40</cell>";

    childStr[1] += "</row>";

    childStr[1] += "<row>";

    childStr[1] += "<cell>Biriyani</cell>";

    childStr[1] += "<cell>3</cell>";

    childStr[1] += "<cell>40.70</cell>";

    childStr[1] += "</row>";

    childStr[1] += "</rows>";

    childStr[1] += "</items>";

   jQuery(”#list”).jqGrid({

    datatype: 'xmlstring',

    datastr : mystr,

    colNames:['Inv No','Date', 'Amount','Tax','Total','Notes'],

    colModel :[

      {name:'invid', index:'invid', width:55, sorttype:'int'},

      {name:'invdate', index:'invdate', width:90, sorttype:'date',

                                                   datefmt:'Y-m-d'},

      {name:'amount', index:'amount', width:80, align:'right',

                                                  sorttype:'float'},

      {name:'tax', index:'tax', width:80, align:'right', sorttype:'float'},

      {name:'total', index:'total', width:80, align:'right', sorttype:'float'},

      {name:'note', index:'note', width:150, sortable:false} ],

    pager: jQuery('#pager'),

    rowNum:10,

    viewrecords: true,

    imgpath: '/jquery/plugins/jqgrid/themes/basic/images',

    caption: 'Table Grid from XML String',

    width:900,

    height:350,

    subGrid: true,

    subGridRowColapsed: function(subgrid_id, row_id) {},

    subGridRowExpanded: function(subgrid_id, row_id) {

    var subgrid_table_id;

    subgrid_table_id = subgrid_id+”_t”;

    //alert(row_id);

    jQuery(”#”+subgrid_id).html(”<table id='”+subgrid_table_id+”' class='scroll'></table>”);

          jQuery(”#”+subgrid_table_id).jqGrid({

              datatype: 'xmlstring',

              datastr : childStr[row_id-1],

              colNames:['Item','Quantity', 'Price'],

              colModel :[

                         {name:'itemid', index:'itemid', width:50, sorttype:'text'},

                         {name:'qtyid', index:'qtyid', width:50, sorttype:'int'},

                         {name:'priceid', index:'priceid', width:50, align:'left',

                                                      sorttype:'float'},

                        ],

              width: 500,

              height:100

          }) //end of child grid

      } //end of subgridrowexpanded

  }); //end of parent grid

 }); //end of document ready

</script>