Button menu problem

hi
i’m trying to make a button menu in AS3. i have several clip-buttons on stage, with instance names.in main timeline i have a activeButton variable that keeps track the name of the selected button.
Inside the clip i wrote the listeners and the functions for the up, over, down states.the problem is with the down function, that triggers when i click the button. the first line is the problem:

function down(e:MouseEvent):void
{
[COLOR=red]MovieClip(this.parent.getChildByName(activeButton)).gotoAndStop(“up”[/COLOR]);
btnLabel.textColor=0xFF0000;
MovieClip(parent).activeButton=this.name;
this.gotoAndStop(“down”);
}
i get an error “activeButton is not a property” or something like that. However, if i put the function in the main timeline, there’s no problem:MovieClip(this.getChildByName(activeButton)).gotoAndStop(“up”)
it works great. why the code inside the function doesn’t work? i’m even casting the information. what’s the problem??
anyone can help, please?