Preloader problem

The preloader works fine when a external.swf is called by a button event I have this button event script :

on (release) {
if(_level0.current_selection == "button"){
stop();
} else {
_level0.containerMC.loadMovie("mymovie01.swf");
 
_level0.preloader.gotoAndStop(2);
 
 
}
}

Now i´m trying to load another external swf without a button event. I have a code frame with a stop() button on main timeline like this:

_root.containerMC.loadMovie("mymovie02.swf");
stopAllSounds();

with this code the external swf can be loaded into the containerMC but the preloader does not work like he does ( does not display precents loaded) as when it is called by a button event.
Could please point me out how to fix this preoblem
thanks in advance