It has something to do with your balloons. Nobody lives out there,

http://pastebin.com/BXeABRiP

I can no longer log into the server, and I just made my quadrupling ore setup I really don't want to lose.

Can this be avoided by using MCEdit to move my player very very far away?

Tried that, and it didn't do anything :(

EDIT: I am on 1.7.10 if that helps, but it was probably obvious from the log.

Something that others claim has worked for them is to change the mob armour spawn rate to 0, start the world once in peaceful mode and change back to your normal difficulty. I've got no idea why this would work, but try it out and let us know if it works. The more data we have on this the better.

Already posted