2012-02-08 10:54:31 [SEVERE] net.minecraft.server.WorldConlictException: Failed to check session lock, aborting
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.WorldNBTStorage.checkSession(WorldNBTStorage.java:74)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.World.l(World.java:2655)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.World.y(World.java:278)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.World.save(World.java:268)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.World.doTick(World.java:1740)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:524)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:435)
2012-02-08 10:54:31 [SEVERE] 	at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)
2012-02-08 10:54:31 [SEVERE] Unexpected exception
net.minecraft.server.WorldConlictException: Failed to check session lock, aborting
	at net.minecraft.server.WorldNBTStorage.checkSession(WorldNBTStorage.java:74)
	at net.minecraft.server.World.l(World.java:2655)
	at net.minecraft.server.World.y(World.java:278)
	at net.minecraft.server.World.save(World.java:268)
	at net.minecraft.server.World.doTick(World.java:1740)
	at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:524)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:435)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)