ActionScript 3.0 :: Very Choppy Preloader - Simulating Download

I made a preloader for this movie: [URL]. But when I simulate a download, it goes straight from 0% to 100% and the bar goes from nothing to filling only half of the screen. I'm using Flash CS3. Here's the code for the Preloader.fla file:

var req:URLRequest = new URLRequest("movie.swf");
var loader:Loader = new Loader();
var nPercent:Number;
loader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, preLoad);
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, fileLoaded);
[Code] .....

The graphic for the preloader is made up of two parts. background_mc is the light blue background for the progress bar and bar_mc is the dark bar that's supposed to fill it up.