Session Lock Issues

I've created a system that creates an NBTTagCompound and saves it in a file in the current save file. Every time a player logs in, it reads from the NBTTagCompound in the file. Every time a player logs out, it writes the NBTTagCompound to the file. If there is no file when it attempts to read the file, it runs the writing method to create a new file with a blank NBTTagCompound. However, while this system works quite well for me, the chunk data will not save due to a session lock error. The error is below.

net.minecraft.world.MinecraftException: The save is being accessed from another location, aborting
[iNFO] [sTDERR] 	at net.minecraft.world.storage.SaveHandler.checkSessionLock(SaveHandler.java:104)
[iNFO] [sTDERR] 	at net.minecraft.world.World.checkSessionLock(World.java:4001)
[iNFO] [sTDERR] 	at net.minecraft.world.chunk.storage.AnvilChunkLoader.saveChunk(AnvilChunkLoader.java:120)
[iNFO] [sTDERR] 	at net.minecraft.world.gen.ChunkProviderServer.safeSaveChunk(ChunkProviderServer.java:232)
[iNFO] [sTDERR] 	at net.minecraft.world.gen.ChunkProviderServer.unload100OldestChunks(ChunkProviderServer.java:328)
[iNFO] [sTDERR] 	at net.minecraft.world.WorldServer.tick(WorldServer.java:166)
[iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:668)
[iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:598)
[iNFO] [sTDERR] 	at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:123)
[iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
[iNFO] [sTDERR] 	at net.minecraft.server.ThreadMinecraftServer.run(ThreadMinecraftServer.java:16)

Does anyone know how to fix this? I've only found one thing relating to this, which is a tutorial by Mithion about saving NBT to files, but it dates back to 1.2.5 and his methods are not working. Thank you in advance for any response!