I suppose this isn't particularly helpful to you...
But I began getting the same error this morning.
Neocodex was down for a while and I thought that was the issue, but when it came back up, I still got this error.
I've tried restarting and reinstalling. I can still log on to Neocodex/Neopets, and I can use the Valorous suite.
I'm running 64-bit Windows 7
EDIT: Darn it, I got sniped.