iTunes won't play one downloaded song (will play others)

[Macintoshgeek]

The tittle is pretty self explanatory. I recently downloaded a bunch of songs, but iTunes refuses to play only one of them. It asks me to authorize the computer to play the song, but when I type in my username and password it says the computer is already authorized and then the song still won't play.
Any ideas?

[Googlyhead]

Deauthorise then reauthorise all devices. Hopefully will clear the blockage!

Or at least re-do the computer's authorisation.