Flash CS3 nextFrame and prevFrame + error message

Hello everyone,

I have really simple question.
Here is a link. http://www.funrise.com/flash

Please click to facts on the menu.
The next button is working but prev button is not working.
Do you know why?

Here is the AS3.


stop();

next_btn.addEventListener(MouseEvent.CLICK, onNextButtonClicked);
prev_btn.addEventListener(MouseEvent.CLICK, onPreviousButtonClicked);
function onNextButtonClicked(e:MouseEvent):void {
if (this.currentFrame == totalFrames) {
gotoAndStop(49);
} else {
nextFrame();
}
}
function onPreviousButtonClicked(e:MouseEvent):void {
if (this.totalFrames == 70) {
gotoAndStop(49);
} else {
prevFrame();
}
}

Thanks,