"click" event is working but "mouseover" event does't work?

var frequency = 3;

stage.enableMouseOver(frequency);

this.btn1.addEventListener("mouseover", fl_MouseOverHandler_4);

function fl_MouseOverHandler_4()

{

  var target = this.button_1;

var tween = createjs.Tween.get(target, {

  loop: false

})

  .to({

  scaleX: 2,

  scaleY: 2,

  }, 1000, createjs.Ease.bounceOut);

}

// This is working>>

this.btn1.addEventListener("click", fl_ClickToHide.bind(this));

function fl_ClickToHide()

{

  var target = this.button_1;

var tween = createjs.Tween.get(target, {

  loop: false

})

  .to({

  scaleX: 2,

  scaleY: 2,

  }, 1000, createjs.Ease.bounceOut);

}