I have struggled so hard to find a cure for this. After trial and errors, thank God, I found a way to preload the main movie with levels all at the same. Some websites preload levels one at a time and it will get annoying for some users to wait every time for a different movie to load. If you follow this tutorial carefully, you should have no problem.

1:

Put a stop(); action in the first Keyframe of the movie(s) being loaded and nothing else. No movie clip, no graphic, no music or picture but just an empty Keyframe and a stop(); action. Then you load the movies you want. You can load all the movies at once or just a few.

2:

Here is the code to preload the movie(s) Put this code on your preloader:

onClipEvent
// Load Three movies loadMovieNum ("Music.swf", 1);
(load) {
   loadMovieNum ("Music.swf", 2); loadMovieNum ("Music.swf", 3);
}
// We devide it by 1000 to get rid of the
onClipEvent (enterFrame) {
   decimal numbers Total =
Math.floor(_level1.getBytesTotal()/1000) + (_level2.getBytesTotal()/1000) + (_level3.getBytesTotal()/1000) + (_root.getBytesTotal()/1000);
   Loaded =
Math.floor(_level1.getBytesLoaded()/1000) + (_level2.getBytesLoaded()/1000) + (_level3.getBytesLoaded()/1000) + (_root.getBytesLoaded()/1000);
Percent = Math.floor((Loaded/Total)*100);
_root.PercentDisplayTwo = int(Loaded)+" KB "+" | "+(Total)+" KB"+" | "+(Percent)+" %";
// Have a frame lable inside the loaded movie so you can park it
// and call it when ever you want

if (Percent == 100) {
   _level1.gotoAndStop("One"); _level2.gotoAndStop("One");
   _level3.gotoAndStop("One"); _root.play(); }
}