iTunes Problem

[stickmaker]

Okay, this is bizarre. Bought a song on iTunes earlier today. When I try to play it a window pops up with a message telling me that I need to authorize the computer to hear it, with fields for my ID and password. When I enter those I get a message saying the computer is already authorized (which it has been for well over a year). When I try to play the track, I'm told I need to authorize the computer. Buh?!

Update: Got a reply by e-mail with a link to instructions. Just delete the bad file and re-download from the Store. Quick, simple and effective. Song works fine, now. Yay!