I jost got this over and over until I removed the given block at 975,61,-50 (see crash log).
Server.log
2013-02-21 10:53:55 [SEVERE] t: Ticking tile entity
2013-02-21 10:53:55 [SEVERE] at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:962)
2013-02-21 10:53:55 [SEVERE] at...