创建带图片链接菜单报错

Cocos2d-x
#1

//add start menu

	cc.MenuItemFont.setFontName("FirstMenu");
	cc.MenuItemFont.setFontSize(20);
	var item1 =  cc.MenuItemFont.create("Start",function(){},this);
            //就下面这个item2 一创建就报这个错
              //CCSprite.js:2653 Uncaught TypeError: Cannot read property 'use' of null
	var item2 = cc.MenuItemImage.create("res/start_N.png","res/start_N.png");
	var menu =  cc.Menu.create(item1,item2);
	menu.alignItemsVertically();
	this.addChild(menu);