error #1010 button has no properties

This is the code the error comes from

//The main menu's instance name is yourMenu.
//Find and replace yourMenu to match that of your menu instance.

stop();
var btnNum:int;
var highlightNum:int = 1;

var menu11Open:Boolean = false;
var menu21Open:Boolean = false;

var bg:MovieClip = new MovieClip();
bg.graphics.beginFill(0x999999, 1);
bg.graphics.drawRect(0, 0, stage.stageWidth, stage.stageHeight);
bg.graphics.endFill();
bg.alpha = 0;
yourMenu.addChildAt(bg, 0);

//on mouse over menus: set btn number, highlight, open menu, close other menus
stage.addEventListener(MouseEvent.MOUSE_OVER, overBtn);
function overBtn(evt:MouseEvent):void {
switch (evt.target) {
case yourMenu.menu11_btn :
btnNum=1;
highlightBtn();
openMenu();
menu11Open = true;
closeOtherMenus();
break;

case yourMenu.menu22_btn :
btnNum=2;
highlightBtn();
openMenu();
menu21Open = true;
closeOtherMenus();
break;
}
};

//when user mouse leaves a button, set the highlight
stage.addEventListener(MouseEvent.MOUSE_OUT, outBtn);
function outBtn(evt:MouseEvent):void {
switch (evt.target) {
case yourMenu.menu11_btn :
highlightNum=1;
break;

case yourMenu.menu22_btn :
highlightNum=2;
break;
}
};

//mouse out of drop-down, ensure all menus close
bg.addEventListener(MouseEvent.MOUSE_OVER, leaveMenu);
function leaveMenu(evt:MouseEvent):void{
if(bg.hitTestPoint(mouseX, mouseY, true)){
closeMenu();
menu11Open = false;
menu21Open = false;
}

}

//functions to open and close menus
function openMenu():void {
yourMenu.menu_tween.menu_down.addTarget(yourMenu.getChildByName("menu" + btnNum), 1);
}

function closeMenu():void {
yourMenu.menu_tween.menu_up.addTarget(yourMenu.getChildByName("menu" + btnNum), 1);
}

//close menus other than the current one
function closeOtherMenus():void {
if(btnNum == 1 && menu21Open){
yourMenu.menu_tween.menu_up.addTarget(yourMenu.menu21, 1);
menu21Open = false;
}
if(btnNum==2 && menu11Open){
yourMenu.menu_tween.menu_up.addTarget(yourMenu.menu11, 1);
menu11Open = false;
}

};

//adds animation based on current and previous button
function highlightBtn():void {
if(btnNum == 1 && highlightNum == 2){
yourMenu.highlight_tween.two_one.addTarget(yourMenu.highlight_mc, 1);
}
if(btnNum == 2 && highlightNum == 1){
yourMenu.highlight_tween.one_two.addTarget(yourMenu.highlight_mc, 1);
}
};

//Assign appropriate button actions for menu items
stage.addEventListener(MouseEvent.CLICK, itemButtons);
function itemButtons(evt:MouseEvent):void {
switch (evt.target) {
case yourMenu.menu11.item11_btn :
trace("Menu 1, button 1");
break;

case yourMenu.Clear_btn:
trace("Clear");
break;
}
};

here is the error message

TypeError: Error #1010: A term is undefined and has no properties.

at Arquitétura_fla::Menuparaacozinha_14/itemButtons()