URGENT : Progress Bar component start showing too late

I'm using the ProgressBar component in a large movie containing a lot of objects, images ecc ...

In the first frame i've put a ProgressBar component managed by the following ActionScript code :

stop();

listener = {path:this};
listener.complete = function()
{
this.path.play();
};
pr_main.mode = "polled";
pr_main.source = _root;
pr_main.addEventListener("complete", listener);


where pr_main is the instance name of the ProgressBar.

Well, when i try to simulate Download, i have to wait like 4-5 seconds for the bar to appear and when it happens, the bar shows that the loading is already at about 50%, and after it starts to work correctly.

Why i'm experiencing this behaviour ?

Thanx to all