AS3 TypeError: Error #1009 - actionscript-3

Question

I am trying to create a web application with multiple scenes, the error appears when I try to access the next scene with a button I created that contains multiple EventListeners for animation purposes.
The Button did bring me to the next scene, but the error still occurs. After tracing and debugging, the error seems to occur at the Mouse_Out event.
I am still very new to AS3, so can someone please explain to me where my code went wrong and if possible, correct the error for me or is there a better way of writting the code? Thanks in advance.
The Error Involved:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at fl.transitions::Tween/setPosition()
at fl.transitions::Tween/set position()
at fl.transitions::Tween()
at Portfolio_fla::MainTimeline/about_btnOut()
My Code:
import flash.events.MouseEvent;
import fl.transitions.Tween;
import fl.transitions.easing.*;
import fl.transitions.TweenEvent;
about_btn.buttonMode = true;
about_btn.mouseChildren = false;
about_btn.alpha = 0.3;
about_btn.addEventListener(MouseEvent.MOUSE_OVER, about_btnOver);
function about_btnOver(event:MouseEvent):void
{
var AboutAlphaOver:Tween = new Tween(about_btn,"alpha",Regular.easeIn,0.3,1,0.1,true);
}
about_btn.addEventListener(MouseEvent.MOUSE_OUT, about_btnOut);
function about_btnOut(event:MouseEvent):void
{
var AboutAlphaOut:Tween = new Tween(about_btn,"alpha",Regular.easeIn,1,0.3,0.1,true);
}
about_btn.addEventListener(MouseEvent.CLICK, about_btnClick);
function about_btnClick(event:MouseEvent):void
{
gotoAndPlay(1,"About");
}

Answer 1

Try to change your Tween code:
var AboutAlphaOut:Tween = new Tween(about_btn,"alpha",Regular.easeIn,1,0.3,0.1,true);
To:
var AboutAlphaOut:Tween = new Tween(event.currentTarget,"alpha",Regular.easeIn,1,0.3,0.1,true);
I'm not sure if it will work (I'm not too familiar with Flash IDE), but I think it's possible that you are getting error because other scene doesn't have a reference to a button. With event.currentTarget, you will search for reference in the event, so it should find it in any case.
BTW: You shouldn't name your variables starting by capital letter. That way you will more easily distinguish objects from classes.