flash as3, Error #1009

Question

I'm making a website that exist out of linked pages. All the pages are on the time line and all the code is in an as3 file. The first page with links works but if I want to place a link on the second frame I get the 1009 error Cannot access a property or method of a null object reference. Because the link doesn't exist on the first frame. This is my code.

package { import flash.display.MovieClip; import flash.events.MouseEvent;

public class Honger extends MovieClip {

    public function Honger():void {

        weten.buttonMode = true;
        weten.addEventListener(MouseEvent.CLICK, onClickWeten);

        spelen.buttonMode = true;
        spelen.addEventListener(MouseEvent.CLICK, onClickSpelen);

        antwoorden.buttonMode = true;
        antwoorden.addEventListener(MouseEvent.CLICK, onClickAntwoorden);


    }

    public function onClickWeten(e:MouseEvent):void {
        this.gotoAndStop("vragen");
    }   

    public function onClickSpelen(e:MouseEvent):void{
        this.gotoAndStop("spel");
    }

    public function onClickAntwoorden(e:MouseEvent):void{
        this.gotoAndStop("sp");

    }

}

}

Does anyone know how to solve this problem within the code?