Won't play song because it says 'computer not authorized'

I have had iTunes on my computer forever. I pre-ordered the new Alter Bridge release. The 4th song became available, so I downloaded it. But when I click on it, it says my computer is not authorized. So i enter my info and it then says "comuter was previously authorzied, it is now re'authorized". But then when I try to play the song again, it says "computer not authorized'. It plays the first 3 songs i got with no problem. And plays all my other songs with no problem. Why?