AS navigating in movie clip

programming flash
1

Hi, ive got a movie clip on stage, and two buttons, one for gping forwards, and one for going backvards. But i can only get them to navigate forwards, and not backwards.
Anyone know what to do?

Heres the code:

To go backwards:

ani.onMouseDown = function() {
_root.container.gotoAndStop(“prevFrame”);
};

To go forward(and this works):

ani.onMouseDown = function() {
_root.container.gotoAndStop(“nextFrame”);
};