Next button in drag and drop button doesnt function - actionscript-3

Question

I am trying to create a drag and drop game. I want to create a next button and it didnt work. If I remove the next button, the drag and drop game works fine but once I add the drag and drop button, then the whole game doesnt function. Here is my code. Can anyone help me?
import flash.events.MouseEvent;
var objectOriginalX:Number;
var objectOriginalY:Number;
answer.buttonMode = true;
answer.addEventListener(MouseEvent.MOUSE_DOWN, pickObject);
answer.addEventListener(MouseEvent.MOUSE_UP, dropObject);
answer1.buttonMode = true;
answer1.addEventListener(MouseEvent.MOUSE_DOWN, pickObject);
answer1.addEventListener(MouseEvent.MOUSE_UP, dropObject);
answer2.buttonMode = true;
answer2.addEventListener(MouseEvent.MOUSE_DOWN, pickObject);
answer2.addEventListener(MouseEvent.MOUSE_UP, dropObject);
answer3.buttonMode = true;
answer3.addEventListener(MouseEvent.MOUSE_DOWN, pickObject);
answer3.addEventListener(MouseEvent.MOUSE_UP, dropObject);
next_btn.buttonMode = true;
next_btn.addEventListener(MouseEvent.CLICK, next_btn);
/*next_btn.addEventListener(MouseEvent.CLICK,next_btn)
next_btn.buttonMode = true;*/
/*stop();
function next_btn(event:MouseEvent):void
{
gotoAndStop(5);
}*/
function pickObject(event:MouseEvent):void
{
event.target.startDrag();
event.target.parent.addChild(event.target);
objectOriginalX = event.target.x;
objectOriginalY = event.target.y;
}
function dropObject (event:MouseEvent):void
{
event.target.stopDrag();
var matchingTargetName:String = event.target.name + "Target" ;
var matchingTarget: DisplayObject = getChildByName(matchingTargetName);
if(event.target.dropTarget != null && event.target.dropTarget.parent == matchingTarget)
{
event.target.removeEventListener(MouseEvent.MOUSE_DOWN,pickObject);
event.target.removeEventListener(MouseEvent.MOUSE_UP,dropObject);
event.target.buttonMode = false;
event.target.x = matchingTarget.x;
event.target.y = matchingTarget.y;
}
else {
event.target.x = objectOriginalX;
event.target.y = objectOriginalY;
}
function next_btn.MovieClip(event:MouseEvent):void
{
gotoAndStop(5);
}
}
stop();