Gave up - closed iTunes, and restarted and all is well - no agreement or anything. Guess it was just confused.
All is well.
I'm trying to buy a song in iTunes. When I enter the password for my Apple ID, just flashes, then brings up the sign in screen again. It won't let me buy the song. I KNOW my password is correct as I verified it on apple.com just now, and needed it to sign in here to leave this posting.
I just purchased a few albums from the Store a few days ago with no problem.