After iTunes upgrade "no longer authorized"

So I upgraded my iTunes software (which I am regreting) and after the upgrade I tried to sync my iPod Nano and it tells me "this computer is no longer authorized..." and I will lose my purchased songs on my iPod. I tried to authorize it and it then tells me "This computer is already authorized". I press OK and it takes me back to the "this computer is no longer authorized..."

HELP please!