net.minecraft.server.v1_7_R3.ExceptionWorldConflict: Failed to check session lock for world located at ./world, aborting. Stop the server and delete the session.lock in this world to prevent further issues.
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.WorldNBTStorage.checkSession(WorldNBTStorage.java:78)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.World.G(World.java:2840)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.ChunkRegionLoader.a(ChunkRegionLoader.java:130)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.ChunkProviderServer.saveChunk(ChunkProviderServer.java:252)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.ChunkProviderServer.unloadChunks(ChunkProviderServer.java:346)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.WorldServer.doTick(WorldServer.java:196)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.MinecraftServer.v(MinecraftServer.java:687)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:284)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:584)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:490)
[20:29:25 WARN]:        at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628)