[Resolvido] Botão avançar voltar

Olá pessoal, preciso de uma ajudinha.

tenho uma galeria de fotos que aparecem thumbs em sequencia que chama um função para ampliação da foto.

Só que preciso além de poder abrir através das thumbs, ter o botão avançar e voltar.

Alguem pode ajudar?

Obrigada desde já!

var myGalleryXML = new XML();
myGalleryXML.ignoreWhite = true;
myGalleryXML.load("gallery.xml");

myGalleryXML.onLoad = function() {

	myImages = myGalleryXML.firstChild.childNodes;
	myImagesTotal = myImages.length;

	thumb_height = myGalleryXML.firstChild.attributes.thumb_height;
	thumb_width = myGalleryXML.firstChild.attributes.thumb_width;

	full_height = myGalleryXML.firstChild.attributes.full_height;
	full_width = myGalleryXML.firstChild.attributes.full_width;

	callThumbs();
	callFullImage(0);

};

function callThumbs() {
	createEmptyMovieClip("container_mc",getNextHighestDepth());
	var clipLoader = new MovieClipLoader();
	var preloader = new Object();
	clipLoader.addListener(preloader);

	for (i=0; i<myImagesTotal; i++) {
 thumbURL = myImages[i].attributes.thumb_url;
 myThumb_mc = container_mc.createEmptyMovieClip(i, container_mc.getNextHighestDepth());
 myThumb_mc._x = thumb_width*i;
 clipLoader.loadClip("thumbs/"+thumbURL,myThumb_mc);

 preloader.onLoadStart = function(target) {
 target.createTextField("my_txt",target.getNextHighestDepth(),0,0,100,20);
 target.my_txt.selectable = false;
 };

 preloader.onLoadProgress = function(target, loadedBytes, totalBytes) {
 target.my_txt.text = Math.floor((loadedBytes/totalBytes)*100);
 };

 preloader.onLoadComplete = function(target) {
 new Tween(target, "_alpha", Strong.easeOut, 0, 100, .5, true);
 target.my_txt.removeTextField();
 target.onRelease = function() {
 callFullImage(this._name);
 };

 };
	}
}

function callFullImage(myNumber) {

	myURL = myImages[myNumber].attributes.full_url;
	myTitle = myImages[myNumber].attributes.title;
	createEmptyMovieClip("fullImage_mc",getNextHighestDepth());

	var fullClipLoader = new MovieClipLoader();
	var fullPreloader = new Object();
	fullClipLoader.addListener(fullPreloader);

	fullPreloader.onLoadStart = function(target) {
 target.createTextField("my_txt",fullImage_mc.getNextHighestDepth(),0,0,200,20);
 target.my_txt.selectable = false;
	};

	fullPreloader.onLoadProgress = function(target, loadedBytes, totalBytes) {
 target.my_txt.text = Math.floor((loadedBytes/totalBytes)*100);
	};

	fullPreloader.onLoadComplete = function(target) {
 new Tween(target, "_alpha", Strong.easeOut, 0, 100, .5, true);
 target.my_txt.removeTextField();
 target.my_txt.text = myTitle;
 };

 fullClipLoader.loadClip("images/"+myURL,fullImage_mc);

}

Tentei fazer assim:

voltar.onRelease = function(){
 if(myNumber == total-1) {
 myNumber=0;
 }
 else {
 myNumber--;
 }
 callFullImage();

	}

}

Mas está dando valor Undefined.