Extjs 4.2+MVC+vs2010

求教Extjs绑定comboBox数据问题...createWindow: function () {
        var desktop = this.app.getDesktop();
        var win = desktop.getWindow('FrmAreaSerach');
        if (!win) {
            win = desktop.createWindow({
                title: '按区域查询',
                width: 300,
                minWidth: 300,
                height: 400,
                items: [{
                    id: 'comboArea',
                    name: 'comboArea',
                    fieldLabel: '选择行政区域',
                    xtype: 'combo',
                    store: store,
                    valueField: 'serviceHall_ID',
                    displayField: 'serviceHall_Name',
                    mode: 'local',
                    emptyText: '请选择区域',
                    hiddenName: 'serviceHall_ID'//取valueField值用form提交后取该id值  
                    //value: '\Views\FormHandler\comboBox.asmx'
                    
                }]
            });        }
        var store = new Ext.data.JsonStore({
            url: "Views/FormHandler/comboBox.asmx/ServerData",
            fields: ['serviceHall_Name', 'serviceHall_ID'],
            listeners: {//为了编辑时设定初始值Ext.getCmp("fwz").setValue(2);  
                load: function () {
                    Ext.getCmp('comboArea').setValue(Ext.getCmp('comboArea').getValue());
                }
            }
        });
        store.load();  
        return win;
    }   /// <summary>
    /// comboBox1 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // 若要允许使用 ASP.NET AJAX 从脚本中调用此 Web 服务，请取消对下行的注释。
    [System.Web.Script.Services.ScriptService]
    public class comboBox1 : System.Web.Services.WebService
    {
        public string  ServerData="[{\"serviceHall_Name\":\"名字1\",\"serviceHall_ID\":\"1\"},{\"serviceHall_Name\":\"名字2\",\"serviceHall_ID\":\"2\"}]";
        [WebMethod]
        public string HelloWorld()
        {
            return "Hello World";
        }
    }
请问哪里出问题了？ExtjsMVC4js