I also get similar to this, sometimes a few times upon startup and players join, and others randomly when players do /home /tp etc.
java.lang.Exception
at net.minecraft.server.Chunk.a(Chunk.java:675)
at net.minecraft.server.Chunk.a(Chunk.java:649)
at net.minecraft.server.ChunkRegionLoader.a(ChunkRegionLoader.java:297)
at net.minecraft.server.ChunkRegionLoader.a(ChunkRegionLoader.java:65)
at net.minecraft.server.ChunkRegionLoader.a(ChunkRegionLoader.java:54)
at net.minecraft.server.ChunkProviderServer.loadChunk(ChunkProviderServer.java:143)
at net.minecraft.server.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:86)
at net.minecraft.server.PlayerInstance.<init>(PlayerInstance.java:26)
at net.minecraft.server.PlayerManager.a(PlayerManager.java:60)
at net.minecraft.server.PlayerManager.addPlayer(PlayerManager.java:99)
at net.minecraft.server.ServerConfigurationManager.c(ServerConfigurationManager.java:149)
at forge.PacketHandlerServer.finishLogin(PacketHandlerServer.java:169)
at forge.PacketHandlerServer.onModListResponse(PacketHandlerServer.java:108)
at forge.PacketHandlerServer.onPacketData(PacketHandlerServer.java:42)
at forge.MessageManager.dispatchIncomingMessage(MessageManager.java:419)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:1381)
at net.minecraft.server.Packet250CustomPayload.handle(SourceFile:46)
at net.minecraft.server.NetworkManager.b(NetworkManager.java:262)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:119)
at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:97)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:651)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:525)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
If any details are required, please post what info you need and i will post it. i have tried to chase down what this is but still cannot find a cause as yet.
(sorry if its nothing to do with op's issue, but looks very similar if not the same)