I've had that happen to me multiple times when I tried to send in a high score. :| The most annoying one was when I got a score that would give me the "Freaked" avatar, sent it, and it gave me this error. It wasn't even late at night, so it can't have been because I crossed the 12:40-line. It was the middle of the day.
Anyway, I've sent screenshots of stuff like this to Neopet's support e-mail, and of course I never get a response. I guess we all just have to live with the pain and a screenie for the memories.
I'd certainly quit... They already get enough money through their sponsors and their ridiculous "neocash"; anything more would be pure greed. And anyway, Neopets is so non-user loyal these days that I wouldn't even consider throwing any money their way.