CS4, AS2, if currentframe action

Spent days trying to figure something out along this line:

on (release){
play();
if (this._currentframe == 17){
_root.box._visible = true;
}
}
Code is on a mc on main timeline. box is mc on main timeline.

on(release){ handlers are only for Button symbols. Not MC. try this

onClipEvent(enterFrame){
onMouseUp = function(){
play();
if (this._currentframe == 17){
root.box.visible = true;
}
}
}