omg, genious. removeMovieClip is AS2, but the equivilant is removeChild.

So for anyone that wants to know how the story ends....here is the code

Code:
var SIM_btn = new startmenu_btn();
addChild(SIM_btn);
SIM_btn.x = 22
SIM_btn.y = 232

SIM_btn.addEventListener(MouseEvent.CLICK, doSIM_BtnClick01);

function doSIM_BtnClick01(e:MouseEvent):void {
	gotoAndPlay("StartSIM");
        removeChild(SIM_btn);
}

Works like a charm Hope this helps someone else out in the future.

You can resolve this one