Strange problem when trying to run a "tween" function from inside a class

1

im trying to make a site navigation that does the following…
1.) on mouse over, the navigation buttons’ alpha will become 0
2.) a small movieclip with an instance name of “movingBar” should follow the X position of the current button being hovered over…

so i have created a custom class for all my buttons:
[LEFT]

package
{
    import flash.display.MovieClip;
    import flash.events.MouseEvent;
    
    public class NavClass extends MovieClip
    {
        public function NavClass()
        {
            addEventListeners();
            this.buttonMode = true;
            this.useHandCursor = true;
        }
        
        public function addEventListeners():void
        {
            this.addEventListener(MouseEvent.MOUSE_OVER, followCursor)
            this.addEventListener(MouseEvent.MOUSE_OUT, removeNavGlow)
        }
        
        function followCursor(event:MouseEvent):void
        {
            this.alpha = 1;
            Object(root).updateBar();
        }

        function removeNavGlow(event:MouseEvent):void
        {
            this.alpha = 0;
        }
    }
}

[/LEFT]
and on the main timeline, here’s the code:
[LEFT]

import fl.transitions.Tween;
import fl.transitions.easing.*;
import fl.transitions.TweenEvent;

var moveBarTween:Tween;
var resizeBarTween:Tween;

function updateBar():void
{
    trace("code running");
    moveBarTween = new Tween(movingBar,"x",Regular.easeOut,movingBar.x,event.target.x,1,true);
    resizeBarTween = new Tween(movingBar,"width",None.easeNone,movingBar.width,event.target.width,1,true);
}

[/LEFT]
if i try to publish the movie, the following error shows:
“1120: Access of undefined property event.”

if i try to comment-out the other two statements like so:
[LEFT]

function updateBar():void
{
    trace("code running");
    //moveBarTween = new Tween(movingBar,"x",Regular.easeOut,movingBar.x,event.target.x,1,true);
    //resizeBarTween = new Tween(movingBar,"width",None.easeNone,movingBar.width,event.target.width,1,true);
}

[/LEFT]
the trace statement works and no errors are reported…

so it means theres some sort of problem with those two statements which i just cant figure out…