remove code

package com{
import flash.display.MovieClip;
import fl.transitions.Tween;
import fl.transitions.TweenEvent;
import fl.transitions.easing.*;
import flash.events.*;
import flash.utils.*;
public class documentClass extends MovieClip{

public var container:MovieClip;
public var menuOpen:Boolean = false;
public var butNames:Array = ["ABOUT","WORK","LAB","CONTACT"];
public var menuButs:Array = new Array();
public var counter:Number = -1;
public var counter2:Number = 4;
public var menuclip:MovieClip;

public function documentClass(){


init();
}
public function init():void{
var theMask:MovieClip = new MovieClip();
addChild(theMask);
for(var a = 0 ; a <20; a++){
var redball = new circle_mc();
theMask.addChild(redball);
logo_mc.mask = theMask;
redball.scaleX = 1;
redball.scaleY = 1;
redball.x = Math.random() * 420;
redball.y = Math.random() * 248;
var launch1 = new Tween( redball, "scaleX", Strong.easeIn, redball.scaleX, 15, 0.5, true );
var launch2 = new Tween( redball, "scaleY", Strong.easeIn, redball.scaleY, 15, 0.5, true );

}
loadMenutab();
}
public function loadMenutab(){
var menutab = new menutab_mc();
addChild(menutab);
menutab.x = -25.0;
menutab.y = 230.0;
menutab.buttonMode = true;

var myTween:Tween = new Tween(menutab, "x", Elastic.easeOut, -25, 0, 3, true);
menutab.addEventListener(MouseEvent.MOUSE_DOWN,menuCall);
container = new MovieClip();
addChild(container);

}
function menuCall(e:Event):void{
if(getMenuOpen() == false){
activateMenu();
}else if(getMenuOpen() == true){
deactivateMenu();
}

}
function activateMenu(){
setMenuOpen(true);
//counter = counter - 1;
var sender = setInterval(launch,200);
function launch(){
counter++;
//trace(counter + " activate");
menuclip = new menuBtn();
container.addChild(menuclip);
menuclip.x = 65.0 + ( counter * 166);
menuclip.y = 230.0;
menuclip.buttonMode = true;
menuclip.scaleX = 0;
//menuclip.label.text = butNames[counter];
menuButs.push(menuclip);
var myTween:Tween = new Tween(menuclip, "scaleX", Elastic.easeOut, 0, 1.0, 1.5, true);
myTween.addEventListener(TweenEvent.MOTION_FINISH, activateButs);

if(counter == 3){
clearInterval(sender);
counter = -1;


}
}
}
function setMenuOpen(tabvalue:Boolean):void{
menuOpen = tabvalue;

}
function getMenuOpen(){
return menuOpen;

}
function deactivateMenu(){
//counter = counter + 1
setMenuOpen(false);

var sender = setInterval(retract,200);
function retract(){

counter--;
trace(counter + " deactivate");
var target = menuButs[counter];
trace(target);
var myTween2:Tween = new Tween(target, "scaleX", Elastic.easeOut, 1.0,0, 0.7, true);
myTween2.addEventListener(TweenEvent.MOTION_FINISH, activateButs);
if(counter == 0){
clearInterval(sender);
//counter2 = 4;
clearMenuButs();
}
//clearMenuButs();
//clearInterval(sender);
}
}
function activateButs(event:TweenEvent):void {
for(var a = 0; a < menuButs.length; a++){
menuButs.addEventListener(MouseEvent.ROLL_OVER,menuRollOver);
menuButs.addEventListener(MouseEvent.ROLL_OUT,menuRollOut);
menuButs.buttonMode = true;
}
}


function menuRollOver(e:Event){

e.target.gotoAndStop(5);

}
function menuRollOut(e:Event){

e.target.gotoAndStop(1);
}
function clearMenuButs():void{
function retractMenu(event:Event):void{
for(var a = 0; a < menuButs.length; a++){
this.removeChild(menuButs);
}
menuButs.length=0;

}
}
}

I am trying to use the movieclip called "tab_mc" as a toggle button. click it to add 4 movieclips to the stage, click it again to remove them. works once then fails.

Unfortunately it is still generating the same error the second time around

TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/removeChild()
at test2_fla::MainTimeline/retractMenu()