Error #1009 when loading SWF with Document Class

Hello,

I have two SWFs, racingPreloader.swf and racingTrack1.swf, the second one has a document class "mains.RaceMain".

racingPreloader.swf is a preloader for racingTrack1.swf, but it doesn't work. Instead, I get the output:

TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at mains::RaceMain()

I tried permitting debugging on both files, and testing it with Shift+Ctrl+Enter, but the output is about the same; it doesn't give me an specific line where the problem is.

Attempting to launch and connect to Player using URL H:\Swifter\racingPreloader.swf

[SWF] H:\Swifter\racingPreloader.swf - 16102 bytes after decompression

[SWF] H:\Swifter\racingTrack1.swf - 41869 bytes after decompression

TypeError: Error #1009: Cannot access a property or method of a null object reference.

    at mains::RaceMain()

Cannot display source code at this location

This is very similar to what happened at this thread, but I couldn't solve my problem after not finding a solution in it.

Here is the code of frame 1 of racingPreloader.swf:

var loader:Loader = new Loader();

loader.load(new URLRequest("racingTrack1.swf"));

loader.contentLoaderInfo.addEventListener(Event.COMPLETE,openSWF);

function openSWF(e:Event) {

    addChild(loader)

}

And here is some of the code at mains.RacingMain class. I omitted most of the code because I believe only these lines are the cause of the problem:

package mains {

     import flash.display.MovieClip;

     //...More import clausses

     public class RaceMain extends MovieClip {

          public function RaceMain() {

                 if(stage==null)

                     this.addEventListener(Event.ADDED_TO_STAGE,main);

                 else

                     main(null);

          }

          private function main(e:Event):void {

             //start the game

          }

     }

}

Thank you.