Preloader for external swf

1

i load a swf in main_mc but the preloader doesnt work.it disappears when i play movie.
waiting for your help.

onClipEvent (load) {
 total = _root.main_mc.getBytesTotal();
}
onClipEvent (enterFrame) {
 loaded = _root.main_mc.getBytesLoaded();
 percent = int(loaded/total*100);
 text = percent+"%";
 gotoAndStop(percent);
 if (loaded == total) {
  _root.gotoAndPlay(2);
 }
}