Definition flash.event could not be found

import flash.utils.Timer;

import flash.event.TimerEvent;

import fl.transitions.Tween;

import fl.transitions.easing.*;

mc1.alpha = 0;

mc2.alpha = 0;

mc3.alpha = 0;

var timer:Timer=new Timer(500,27);

timer.addEventListener(TimerEvent.TIMER,timerListener);

timer.start();

function timerListener(event:TimerEvent):void

{

  if(timer.currentCount == 1)

  {

  if(count==1)

  {

  var tween6:Tween = new Tween(mc3,"alpha",Strong.easeOut,1,0,1,true);

  }

  var tween1:Tween = new Tween(mc1,"alpha",Strong.easeOut,0,1,2,true);

}

if(timer.currentCount == 10)

{

  var tween2:Tween = new Tween(mc1,"alpha",Strong.easeOut,1,0,1,true);

  var tween3:Tween = new Tween(mc2,"alpha",Strong.easeOut,0,1,2,true);

}

if(timer.currentCount == 19)

{

  var tween4:Tween =new Tween(mc2,"alpha",Strong.easeOut,1,0,1,true);

  var tween5:Tween =new Tween(mc3,"alpha",Strong.easeOut,0,1,2,true);

}

if(timer.currentCount == 27)

{

  timer.reset();

  timer.start();

  var count = 1;

}

this is what i get ....