Code error 1009. Not sure how to fix. noobie here

i am having trouble with two codes i have inside my project.
to give as many details i can, i have a labels layers home, threeD, art, digitalArt, and pcCaseMod. i have an actions layer below the labels layer. then below that my content layer with all my content.
this code is on the actions layer under home:

[COLOR=Blue]stop();

// Start Main Nav

function openLabel(event:MouseEvent):void {
switch (event.currentTarget) {
case home_btn :
gotoAndStop(“home”); [COLOR=Red]this is on key 1[/COLOR]
break;
case threeD_btn :
gotoAndStop(“threeD”); [COLOR=Red]this is on key 20[/COLOR]
break;
case art_btn :
gotoAndStop(“art”); [COLOR=Red]this is on key 40[/COLOR]
break;
case digitalArt_btn :
gotoAndStop(“digitalArt”); [COLOR=Red] this is on key 60[/COLOR]
break;
case pcCaseMod_btn :
gotoAndStop(“pcCaseMod”); [COLOR=Red]this is on key 80[/COLOR]
break;

    }

}

home_btn.addEventListener(MouseEvent.CLICK, openLabel);
threeD_btn.addEventListener(MouseEvent.CLICK, openLabel);
art_btn.addEventListener(MouseEvent.CLICK, openLabel);
digitalArt_btn.addEventListener(MouseEvent.CLICK, openLabel);
pcCaseMod_btn.addEventListener(MouseEvent.CLICK, openLabel);

// End Main Nav[/COLOR]

on the actions “threeD” key , i have this code to do a page flip within that section: i did remove the stop(); to see if that cuased it and it was not the problem.

[COLOR=Blue]stop();[/COLOR]
[COLOR=Blue]
import fl.transitions.Tween;
import fl.transitions.easing.Strong;
import fl.transitions.TweenEvent;

container.sidea.flip.addEventListener(MouseEvent.CLICK,onflip);
container.sideb.flip.addEventListener(MouseEvent.CLICK,onflip);
addEventListener(Event.ENTER_FRAME,loop);

var isStill:Boolean=true;
var arraytween:Array = new Array();

function onflip(e:Event) {
if (isStill) {
arraytween.push(new Tween(container,‘rotationY’,Strong.easeOut,container.rotationY,container.rotationY+180,1,true));
arraytween[0].addEventListener(TweenEvent.MOTION_FINISH,reset);
isStill=false;

}
}
function reset(e:Event) {
isStill=true;
arraytween=[];

}

function loop(e:Event) {

[COLOR=Lime] if (container.rotationY>=90 && container.rotationY<=270) {[/COLOR]
container.addChild(container.sideb);
container.scaleX=-1;
} else {
container.addChild(container.sidea);
container.scaleX=1;
}
if (container.rotationY>=360) {
container.rotationY=0;
}

}[/COLOR]

when i debug the movie,i clicked on the threeD button, then the art button. after the click on the art button this message pops up: Error #1009: Cannot access a property or method of a null object reference.
at threeD/loop()[threeD::frame20:30]

the line i wrote in green is were the error is stemming.

im really new to this.