dispatchEvent to fire MouseEvent not working

Question

I am adding the same image (play button) to a movie clip those images later when pressed toggle states and play a video.

What I am trying to accomplish is automatically toggle the default image since that video is playing automatically.

        //Setup thumb Container
         thumbs = new Sprite();
        thumbs.addEventListener (MouseEvent.CLICK, playVideo);
        thumbs.x = thumbs_x;
        thumbs.y = thumbs_y;
            thumbs.buttonMode = true;
            main_container.addChild (thumbs);
    //Call Function that gets all the thumbs using loader and adds it to the thumb movieClip

    callThumbs ();
    setDefaultButton ();

    function callThumbs ():void {



        for (var i:Number = 0; i < my_total; i++) {



                var thumb_url = my_videos[i].@THUMB;
                var thumb_loader = new Loader();
                thumb_loader.name = i;
                trace(thumb_loader.name);
                thumb_loader.load (new URLRequest(root_path + thumb_url));
                thumb_loader.contentLoaderInfo.addEventListener (Event.COMPLETE, thumbLoaded);
                thumb_loader.y = (thumb_height+210)*i;

    }

        function thumbLoaded (e:Event):void {
        var my_thumb:Loader = Loader(e.target.loader);
        thumbs.addChild (my_thumb);
    }


function setDefaultButton ():void {
thumbs.getChildAt(0).dispatchEvent(new MouseEvent(MouseEvent.CLICK));
//or 
thumbs.getChildByName('0').dispatchEvent(new MouseEvent(MouseEvent.CLICK));
}

So this does the same thing as click the first image but it happens automatically.

THIS IS MY ERROR:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at LowesPlayerCS4_fla::MainTimeline/setDefaultButton()
    at LowesPlayerCS4_fla::MainTimeline/processXML()
    at flash.events::EventDispatcher/dispatchEventFunction()
    at flash.events::EventDispatcher/dispatchEvent()
    at flash.net::URLLoader/onComplete()

Answer 1

Try adding the thumb_Loader to the Display List in callThumbs rather than thumbLoaded.