My drop down menu is not working

Trying to build a dropdown menu… i have menu_mc on my main stage. Menu_mc is an instance of movieClip menu… subBut1_mc is a instance of clip subBut1 on the menu movieClip.

my actionScript on the main stage is:

this.menu_mc.onRollOver = function() {
menu_mc.gotoAndPlay("_over");
trace(“over”);
}
this.menu_mc.onRollOut = function() {
menu_mc.gotoAndPlay(_down);
trace(“out”);
}
menu_mc.subBut1_mc.onRollOver = function() {
trace(“but1”);
}

PROBLEM: the first 2 traces are working but the last one is not…

what am i doing wrong…