Server Crashing (Even with no plugins)

Putting up a server for me and some friends to practice UHC on, and I am getting this error:


java.lang.RuntimeException: Failed to check session lock, aborting
at net.minecraft.server.v1_7_R1.WorldNBTStorage.h(WorldNBTStorage.java:57)
at net.minecraft.server.v1_7_R1.WorldNBTStorage.<init>(WorldNBTStorage.java:42)
at net.minecraft.server.v1_7_R1.ServerNBTManager.<init>(SourceFile:16)
at net.minecraft.server.v1_7_R1.MinecraftServer.a(MinecraftServer.java:216)
at...

Server Crashing (Even with no plugins)