There is a hard cutoff each night at 12:40 AM NST. If you have opened your game prior to this time, and submit the score after this time, you will receive an error that states: Problems processing your score, etc. etc.
There's no way around that.
This does not sound like the issue you are describing. You say your score showed completely accepted, no error, no review, and it still did not show up on the high score table? In that case, it would have to be some sort of issue with either a busy server on Neopets side, or potentially heavy traffic on a proxy if your using one. In either case, you would receive the same: Problem processing your score error.
Other than that, it could be a one in a million glitch of some sort if it still hasn't shown up. I've played a lot of games in my day and never ran into this particular issue. =/