ActionScript 3 Flash error 1009 and 2025 combo box - actionscript-3

Question

Im trying to insert a music using combo box from the component asset. yesterday works fine, but today suddenly it stopped working and it gave me this error:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
everytime I clicked on the combo box these error appears, strangely it works fine yesterday.
this is the code for the first frame:
import flash.events.Event;
import flash.events.MouseEvent;
import flash.system.fscommand;
import flash.media.Sound;
import flash.media.SoundChannel;
import flash.net.URLRequest;
import flash.events.Event;
import flash.media.SoundTransform;
import flash.events.MouseEvent;
//Declare MUSIC Variables
var musicSelection:Sound;
var musicChannel:SoundChannel;
var musicTrack:String = "music/dearly_beloved.mp3";
var musicVolume:Number=0.2;
/*var isMuted = false;*/
loadMusic();
function loadMusic():void
{
//first stop old sound playing
SoundMixer.stopAll();
musicSelection = new Sound();
musicChannel = new SoundChannel();
//create and load the required soun
musicSelection.load(new URLRequest(musicTrack));
//when loaded - play it
musicSelection.addEventListener(Event.COMPLETE, musicLoaded);
}
function musicLoaded(evt:Event):void
{
//finished with this listener
musicSelection.removeEventListener(Event.COMPLETE, musicLoaded);
//play music
playMusic();
}
function playMusic():void
{
//play the random or selected music
musicChannel = musicSelection.play();
//setting the volume control property to the music channel
musicChannel.soundTransform = new SoundTransform(musicVolume, 0);
//but add this one to make repeats
musicChannel.addEventListener(Event.SOUND_COMPLETE, playAgain);
}
function playAgain(evt:Event):void {
// remove this listener and repeat
musicChannel.removeEventListener(Event.SOUND_COMPLETE, playAgain);
playMusic();
}
and this is the code for the second frame:
import flash.events.Event;
menuBtn.addEventListener(MouseEvent.CLICK, goToMenu)
function goToMenu(evt:Event):void
{
gotoAndPlay(2);
}
// BUTTON EVENT LISTENERS
musicCombo.addEventListener(Event.CHANGE, updateMusic);
volumeSL.addEventListener(Event.CHANGE, setSlider);
//process COMBO BOX changes
function updateMusic(evt:Event):void
{
if (musicCombo.selectedItem.data == "none")
{
//no music is required so stop sound playing
SoundMixer.stopAll();
}
else
{
//otherwise load in the selected music
musicTrack = "music/" + musicCombo.selectedItem.data;
loadMusic();
}
}
function setSlider(evt:Event):void
{
//identify the button clicked
var mySlider:Object = (evt.target);
//adjusting to volume of the music channel
musicVolume = mySlider.value;
musicChannel.soundTransform = new SoundTransform(musicVolume, 0);
}
the error occurs whenever I clicked on the combo box and when I tried to insert another combo box without putting any data, the same error occurs. hope you guys can help me ASAP cause this is due on friday this week xD
thanks

Answer 1

Alright, found the answer. It seems I need to put these 3 lines of code:
import fl.events.ComponentEvent;
import fl.controls.ComboBox;
import fl.data.DataProvider;