Apple TV is not accepting my iTunes account name or password. I can sign in on my Mac and transfer purchases/rentals over to the Apple TV, but that's pretty time-consuming, compared to doing it right on the Apple TV. It used to work perfectly, now it just doesn't-- no matter how many times I type in the name/password. Everything else is fine, I just can't get into the iTunes store.
The country is set correctly, my wireless network is set correctly (and working), my name/password is correct, I "agreed" to the latest terms, YouTube works fine ... it just won't accept my name/password.
Can you actually browse store content or do you just fail at purchasing?
If not maybe the store is down - AppleTV may not connect to exactly the same store address as iTunes, so iTunes working is not necessarily a sign that the AppleTV 'area' is up.
Have you tried unplugging/rebooting?
Convenience and HD rentals aside I find iTunes more reliable for purchasing YMMV.