Please Help!! There is an error in my drop down list

The error message shows 1120: Access of undefined property event

This is the code:

import flash.filters.GlowFilter;

var navBtnGlow: GlowFilter = new GlowFilter(0x999999, 0.8, 0, 15, 1, 2, false, false);

mcNavBar.addEventListner(MouseEvent.MOUSE_OVER, navOverF);

mcNavBar.addEventListner(MouseEvent.MOUSE_OUT, navOutF);

function navOverF (event:MouseEvent): void {

  event.target.filters = [navBtnGlow];

}   mcNavBar.setChildIndex (event.target as MovieClip, 1);

    Dropdown.gotoAndStop(mcNavBar.getChildAt (1).name);

function navOutF (event:MouseEvent): void {

  event.target.filters = [];

}