Board Thread:The Quarters - Q & A/@comment-24660057-20140309041253/@comment-1873666-20140310171448

Judging from prior discussion on github, ending a very large challenge can be hard on the server. Hattishoe was able to do it recently, so I might try once more, particularly at a time when nearly no one is online. (Expect a delay, and if it fails, ping an admin before retrying.)

I suggest putting out a ticket or talking to lefnire, as he explained the risk, and he mentioned here that he's working on similar issues.

If you're filing a ticket, I'd suggest posting it here.