I've been having the exact same problem. No clue what the problem is or how to fix it but I have found that if I make a copy of the file (in Finder; trying to copy it in itunes actually resulted in a shortened version of the song...), the copy version seems to play fine. Suffice it to say, it's a bit of a pain to go through and manually copy each file so I've actually been using file conversion software (I use XLD; it's free and pretty simple to do multiple albums in one go; I'm sure any other'd work fine too). Output format doesn't seem to matter, it really does just seem to be a question of creating a new file. Again, this is less of a fix and more of a work-around but I hope it's useful; if anyone knows what the actual problem is/how to fix it, that'd be much appreciated!!