求助，EXT的Tree

页面

<div id="main-ct" style="width:100%;height:100%;"></div>

脚本

Ext.onReady(function(){
    var xt = Ext.tree;

    // turn on quick tips
    Ext.QuickTips.init();

    var cview = Ext.DomHelper.append('main-ct',
        {cn:[{id:'main-tb'},{id:'cbody'}]}
    );


    // create our layout
    var layout = new Ext.BorderLayout('main-ct', {
        center: {
            title:'Components',
            margins:{left:3,right:3,bottom:3,top:3}
        }
    }, 'main-ct');

    layout.batchAdd({
       center : {
           el: cview,
           autoScroll:true,
           fitToFrame:true,
           resizeEl:'cbody'
       }
    });



    // the component tree
    var ctree = new xt.TreePanel('cbody', {
        animate:true,
        enableDD:true,
        containerScroll: true,
        lines:false,
        rootVisible:false
    });


    var croot = new xt.AsyncTreeNode({
        allowDrag:false,
        allowDrop:false,
        id:'croot',
        text:'Packages and Components',
        cls:'croot',
        loader:new Ext.tree.TreeLoader({
            dataUrl:'/tmp1.json'
        })
    });
    ctree.setRootNode(croot);
    ctree.render();
    croot.expand();

});

JSON文件

[{"text":"profil1@anonyme.ca",
   "id":"10\/1",
   "cls":"cmp",
   "leaf":false,
   "children":[{"text":"Favoris",
                     "id":"10\/1\/favoris",
                     "cls":"cmp",
                     "leaf":false,
                     "children":[{"text":"une Fiche",
                                       "id":"10\/1\/favoris\/idFiche",
                                       "cls":"cmp",
                                       "leaf":true,
                                       },
                                     {"text":"un sous-dossier de Favoris",
                                       "id":"10\/1\/favoris\/sousDossier",
                                       "cls":"cmp",
                                       "leaf":false, 
                                       "children":[{"text":"une Fiche",
                                                         "id":"10\/1\/favoris\/idFiche",
                                                         "cls":"cmp",
                                                         "leaf":true}]
                                      }]
                     },
                     {"text":"Poubelle",
                       "id":"10\/1\/poubelle",
                       "cls":"cmp",
                       "allowDrop":true,
                       "leaf":true}
                     ]
}]

我运行这个例子，在firefox下正常显示，而IE下却什么都不显示，看一下。谢谢了