From the error, it could look like a corrupted chunk has caused it, possibly in the spawn chunks. I can't promise when I'll look deeper into it or fix it right now.
Meanwhile, you can all entertain yourself with some statistics from the crash report folder
Edit: It looks like it's a spawn area chunk in The Nether. Anyone's done anything important recently? Otherwise we should probably just roll The Nether spawn area back a bit to earlier in January.
Edit: I've rolled back the Nether spawn area about a week which fixed the problem, but another error is preventing the server from starting up, so you still can't play on it.
Edit: There was a corrupted zombie in a spawn chunk in the overworld too which caused the second error. This region file has also been rolled back and the server works now.