Ext.data.GridPanel is not constructor 错误如何处理?

   <script type="text/javascript">

     Ext.onReady(function(){

   var _grid=new Ext.data.GridPanel({
        renderTo:Ext.getBody(),
        store:new Ext.data.JsonStore({
                      data:[{name:"余学武",age:31,sex:"男"},{name:"方丽",age:27,sex:"女"}],
                      fields:["name","age","sex"]
              }),
        columns:[{header:'姓名',indexData:'name'},{header:'年龄',indexData:'age'},{header:'性别',indexData:'sex'}]
       });

   });


</script>

问题补充
找了很久都没有找到错在那里，请各位老大帮忙看看，谢谢了

对象搞错了！应该是
Ext.grid.GridPanel