totalFrames of dynamically loaded swf

I've been trying for 2 days now to find the total number of frames of a dynamically loaded .swf.

Here's an example code:

var loader:Loader = new Loader;
loader.load(new URLRequest("mop.swf"))
master_mc.addChild(loader);
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, xmlLoadedF);
function xmlLoadedF(event:Event):void

{
    trace(loader.content.totalFrames);
}

I am truly puzzled.

Any help would be greatly appreciated.