ActionScript 3.0 :: Flash Hangs While Loading Xml?

I have a xml file with size of 550kb. when I load it in the simplest way flash player hangs, while it is loading, than it runs normally here is the code
 
var loader:URLLoader = new URLLoader();var req:URLRequest = new URLRequest();
but.addEventListener(MouseEvent.CLICK, onClick);
function onClick(e:MouseEvent):void{ loader.addEventListener(Event.COMPLETE, onXmlLoad) loader.load(req);}
function onXmlLoad(e:Event):void{ trace(e.target.data)}