Add Thumbnail Button question

I’ve done the turoial for xml gallery with thumbnails. I modified it to add some animations and my prev/next buttons are now inside of a movie clip. They don’e work any more. None of the code has change just the positio of the buttons in my movie.

Here is a piece of the code that makes the buttons work.

listen = new Object();
listen.onKeyDown = function() {
if (Key.getCode() == Key.LEFT) {
prevImage();
} else if (Key.getCode() == Key.RIGHT) {
nextImage();
}
};
Key.addListener(listen);
previous_btn.onRelease = function() {
prevImage();
};
next_btn.onRelease = function() {
nextImage();
};

According to what I understand from the tutorial, this function uses instance names. The buttons should work no matter where the buttons are in the movie.