Originally posted by MacBandit
Was it an AAC file you downloaded from Apple or one you created yourself? I'm sure you know that Apple has put a DRM(Digital Rights Management) in there AAC files.
There are players for windows machines that will play MP4 AAC files but you have to get them. Also there are plug-ins for existing MP3 players. Simply put you can't play an MP4 AAC file on just any MP3 player it someone has to set it up to play them. Also MP4s are incompatible with portable MP3 players unless stated otherwise. MP3s and MP4s are completely different and incompatible formats.