Json数据如何载入到store再在Ext.GridPanel中显示

部分代码：
var proxy= new Ext.data.HttpProxy({url:'Data_GetStu.aspx'});  
var stu= new Ext.data.Record.create([      
                     {name: 'id',mapping:'id'},
                     {name: 'name',mapping:'name'},
                     {name:'score',mapping:'score'},
                     {name:'fee',mapping:'fee'}                     
                      ]);         
var reader = new Ext.data.JsonReader({root:'data',totalProperty:'totalCount'},stu);
 var store = new Ext.data.JsonStore({
   proxy: proxy,    
       reader:reader                       
});         

store.load();Data_GetStu.aspx返回的数据是：
{totalCount:5,success:true,error:"",singleInfo:"",data:[{"id":"1 ","name":"Dick ","score":"99 ","fee":"990 "},{"id":"2 ","name":"Fenando ","score":"88 ","fee":"880 "},{"id":"3 ","name":"Steve ","score":"77 ","fee":"770 "},{"id":"4 ","name":"Locker ","score":"66 ","fee":"660 "},{"id":"5 ","name":"Eli ","score":"55 ","fee":"550 "}]}
GridPanel能在网页中正确显示，但是数据就是无法载入网页。。蛋疼。。疯掉了就要。。运行后错误提示：
'this.fields'为空或对象不正确