About content property

1

i read this tutorial, it is about how to control the time line of the loaded swf

http://www.flepstudio.org/forum/tutorials/483-tips-abd-tricks-actionscript-3-0-loader-content.html

but i get this error:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at main_fla::MainTimeline/frame1() :diss:


var url:URLRequest = new URLRequest("play.swf");
var swfLoader:Loader = new Loader();
swfLoader.load(url);
addChild(swfLoader);

var movie:* =swfLoader.content;
var clip:MovieClip = movie;
clip.gotoAndStop(5);

any help