Помогите исправить ошибку

Уже 2 раза вылетает такая ошибка, с откатом сервера:

Спойлер

net.minecraft.server.WorldConlictException: Failed to check session lock, aborting
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.WorldNBTStorage.checkSession(WorldNBTStorage.java:77)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.World.m(World.java:2743)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.World.A(World.java:266)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.World.save(World.java:255)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.World.doTick(World.java:1770)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:555)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:457)
2013-03-05 10:55:00 [SEVERE]at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
2013-03-05 10:55:00 [SEVERE] Unexpected exception
net.minecraft.server.WorldConlictException: Failed to check session lock, aborting
at net.minecraft.server.WorldNBTStorage.checkSession(WorldNBTStorage.java:77)
at net.minecraft.server.World.m(World.java:2743)
at net.minecraft.server.World.A(World.java:266)
at net.minecraft.server.World.save(World.java:255)
at net.minecraft.server.World.doTick(World.java:1770)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:555)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:457)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)

Из-за чего это может быть и как устранить ошибку?