求助Ext Grid无法显示数据


为什么我的ext Grid可以显示，但是没有数据显示。求助大家看看我的问题吧后台代码：返回数据如下：{'data':[{'OrderID':100,'Username':'linrd ','StatusID':1,'CreateTime':2010/7/31 21:10:13,'SubTotal':800.00},{'OrderID':101,'Username':'linrd ','StatusID':11,'CreateTime':2010/8/1 9:08:01,'SubTotal':1350.00}],'totalCount':1000}
代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using Service;
using System.Xml;
using System.Text;
public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        StringBuilder jsonStr = new StringBuilder();
        jsonStr.Append("{'data':[");
        SqlConnection conn =new SqlConnection("server=.;database=ExtShop;uid=sa;password=123");
         string sqlstr = "select *from T_Orders";
        try
        {
            conn.Open();
            SqlCommand comm = new SqlCommand(sqlstr, conn);    
            SqlDataReader rd = comm.ExecuteReader();
            while (rd.Read())
            {
                jsonStr.Append("{");
                jsonStr.Append("'OrderID':" + rd.GetInt32(0).ToString() + ",");
                jsonStr.Append("'Username':'" + rd.GetString(1) + "',");
                jsonStr.Append("'StatusID':" + rd.GetInt32(3).ToString() + ",");
                jsonStr.Append("'CreateTime':" + rd.GetDateTime(2) + ",");
                 jsonStr.Append("'SubTotal':" + rd.GetSqlMoney(4).ToString() + "");
                jsonStr.Append("},");
            }
        }
        finally
        {
            conn.Close();
        }
        jsonStr.Remove(jsonStr.Length - 1, 1);
        jsonStr.Append("],'totalCount':1000}");
        Response.Write(jsonStr);
    }
}js代码如下：
Ext.onReady(function () {
    Ext.QuickTips.init();
    var sm = new Ext.grid.CheckboxSelectionModel();
    var cm = new Ext.grid.ColumnModel([
        new Ext.grid.RowNumberer(),
        sm,
        { header: 'OrderID', dataIndex: 'OrderID', align: 'center', width: 100 },
        { header: 'Username', dataIndex: 'Username', width: 100 },
        { header: 'StatusID', dataIndex: 'StatusID', align: 'center', width: 100 },
        { header: 'CreateTime', dataIndex: 'CreateTime', align: 'center', width: 100 },
        { header: 'SubTotal', dataIndex: 'SubTotal', align: 'center', width: 100 }
    ]);
    cm.defaultSortable = true;
    var ds = new Ext.data.Store({
        autoLoad: true,
        proxy: new Ext.data.HttpProxy({ url: 'Default2.aspx' }),
        reader: new Ext.data.JsonReader({
            root: 'data',
            totalProperty: 'totalCount'        }, ['OrderID', 'Username', 'StatusID', 'CreateTime', 'SubTotal']
            )
    });
    ds.load({ params: { start: 0, limit: 25} });
    var grid = new Ext.grid.GridPanel({
        el: 'content',
        data: ds,
        cm: cm,
        height: 400,
        title: '<font size=4,align="center">订单后台</font>',
        bbar: new Ext.PagingToolbar({
            pageSize: 25,
            store: ds,
            displayInfo: true,
            displayMsg: '显示第 {0} 条到 {1} 条记录，一共 {2} 条',
            emptyMsg: "没有记录"
        })
    });
    grid.render();});html代码如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <link rel="stylesheet" type="text/css" href="css/ext-all.css" />    
    
    <script type="text/javascript" src="js/ext-base.js"></script>
    <script type="text/javascript" src="js/ext-all.js"></script>
    <script type="text/javascript" src="js/ext-lang-zh_CN.js"></script>
        <script type="text/javascript" src="js/ADOGRID.js"></script></head>
<body>
<div id="content" style="height: 500px;"></div></body>
</html>