Every time I try to play certain songs, it will say that my computer is not authorized to play that song

Every time I try to play certain songs, it will say that my computer is not authorized to play that song. And will have me "authorize" it by plugging in my username and password. Then it will say my computer is authorized so I wait for song to play and it repeats the process. Only certain songs do it. They won't play on my ipod either.

[Re-Titled by Moderator]