audioPlayerDidFinishPlaying not being called at end of audio

Hi,

I have implemented the AVAudioPlayerDelegate in my header file.

#import <AVFoundation/AVAudioPlayer.h>

@interface PlayAudioViewController : UIViewController<AVAudioPlayerDelegate>{
...}

I've also implemented the delegate method in the implementation file:

-(void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player succesfully:(BOOL) flag
{
if(flag == YES)
{
self.playButton.enabled = YES;
}
}

But for some reason the audioPlayerDidFinishPlaying method is not being called. I've read through the documentation and can't figure out why?