Server Crash

We are building on a private server.

Everytime when the player Honigschnitte joined, the server crashed after a minute.

He can't do anything and also sees just not rendered chunks.

Other players can still walk and play normal, but after the server crashed, everything done while Honigschnitte was on is deleted.

See Log

[Server thread/ERROR]: This crash report has been saved to: /games/ni292312_1/ftproot/minecraft/./crash-reports/crash-2014-10-24_17.21.25-server.txt