ExtJs 中的itemselector ，求解

先上代码var ds = new Ext.data.JsonStore({
        listeners: {
            beforeload: function () {
                this.baseParams = {
                    "method": "QueryCountry",
                    "MERCHANTID": '<%=Session["strMerchant"] %>'
                };
            }
        },
        url: "../handler/ConfigTradCountry.ashx",
        root: "ResultData",
        totalProperty: 'TotalRecord',
        fields: ["COUNTRYISO2", "COUNTRYNAME"],
        sortInfo: {
            field: 'COUNTRYNAME',
            direction: 'ASC'
        }     
    });
    ds.load();
    var isForm = new Ext.form.FormPanel({
        id: "isForm",
        title:'交易国家配置',
        
        width: 700,
        bodyStyle: 'padding:10px;',        items: [{
            xtype: 'itemselector',
            name: 'itemselector',
            fieldLabel: '请选择',
            imagePath: '../resources/images/',
            multiselects: [{
                width: 250,
                height: 180,
                store: ds,
                displayField: 'COUNTRYNAME',
                valueField: 'COUNTRYISO2'
            }, {
                width: 250,
                height: 180,
                store: [],
                tbar: [{
                    text: '清除所有',
                    handler: function () {
                        isForm.getForm().findField('itemselector').reset();
                    }
                }]
            }]
         }],
        buttons: [{
            text: 'Save',
            handler: function () {
                if (isForm.getForm().isValid()) {
                    Ext.Msg.alert('Submitted Values', 'The following will be sent to the server: <br />' +
                        isForm.getForm().getValues(true));
                }
            }
        }]
    });效果图为没有滚动条，右边还显示不出来，那位大哥能帮下小弟，谢谢