I do know that Magister Frost has made changes to the Undercroft with new themes/colors for the screen and is perhaps still in the process of re-vamping the entire site. This could be blocking any new members from joining...not sure.
Anyway, I just logged in with no problem and other folks have recently made posts. If the issue persists, you might want to attempt contacting Magister Frost via a PM. I don't know what else to suggest to you.