non posso testare e quindi non sono sicura ma... prova a mettere questo

codice:
// Event handler for 'Next slide' button 
next_btn.onRelease = function() { 

holder.onEnterFrame = function(){
	if(currentSlideNode._alpha>0){
	currentSlideNode._alpha-=5
	}
	if(currentSlideNode._alpha<=0){
	
		var nextSlideNode; 

		nextSlideNode = currentSlideNode.nextSibling; 
		if (nextSlideNode == null) { 
			break; 
		} else { 
		//Display current slide number on Scene 
			currentIndex++; 
			updateSlide(nextSlideNode); 
			currentSlideNode = nextSlideNode; 
		} 
	}
}
};
sperem.