Loading and controlling a movie through actionscript

Hi im currently working on a new project that requires me to control a movie clip through actionscript. The problem is that i have to attach a movie clip symbol onto another movie clip after i select the specific clip i want to play.

E.g
playbox is the movie Clip i attach other clips on.
A is the movie Clip to be attached.

So i have this going on right now on a button.

on(release){
playbox.attachMovie(“A”,“movie”,2);
}

This works fine as the movie starts to play however the question is how do i use gotoAndPlay(10) on the attached movie clip? I am required to control what frames A has to be at and playbox.gotoAndPlay(10) doesnt seem to function.

Please advise, thanks!