Preloader bugging

programming flash
1

Hi, I have some problem with a preloader in AS3.
Here is the error I got.

TypeError: Error #1009: Il est impossible d'accéder à la propriété ou à la méthode d'une référence d'objet nul.
	at bugwithloading_fla::MainTimeline/PL_LOADING()

Here is the litteral traduction :

TypeError: Error #1009: It's impossible to acces to the propriety or the method of a refered null object.
	at bugwithloading_fla::MainTimeline/PL_LOADING()

here is the .fla

The strange thing is that I did it with a tutorial, and the loaded info was a flv. I don’t have any bug with this one, and the code is the same.