Solved Server Crashing On World Generation

I don't know what's going on, but I am generating a new world and my server keeps crashing. I am using the most updated recommended version of Bukkit (1.6.4-R2.0), so I know it is not the version of Bukkit. This is the code:

Code:

Bukkit.getServer().createWorld(new WorldCreator("simons").environment(World.Environment.NORMAL));

Can anyone shed some light on this? Thanks!

Note: I should also say this is the error right before the server crashes:

Code:

java.lang.IllegalStateException: TickNextTick list out of synch
    at net.minecraft.server.v1_6_R3.WorldServer.a(WorldServer.java:491)
    at net.minecraft.server.v1_6_R3.WorldServer.doTick(WorldServer.java:199)
    at net.minecraft.server.v1_6_R3.MinecraftServer.t(MinecraftServer.java:566)
    at net.minecraft.server.v1_6_R3.DedicatedServer.t(DedicatedServer.java:227)
    at net.minecraft.server.v1_6_R3.MinecraftServer.s(MinecraftServer.java:488)
    at net.minecraft.server.v1_6_R3.MinecraftServer.run(MinecraftServer.java:421)
    at net.minecraft.server.v1_6_R3.ThreadServerApplication.run(SourceFile:583)

 

don't load a world from a other thread than the main thread

 

What do you mean by the "main" thread?

 

Most of bukkit is single thread, everythings (with a few exceptions) needs to get invoked by this thread, if it won't be started by this thread it can generate weird bugs later that doesn't give a clue how they are caused.
If you generating your world inside a command, and you aren't doing anything special with the bukkit scheduler, there may be another plugin thats bad stuff on the wrong thread.

A more advanced explenation is given on http://wiki.bukkit.org/Scheduler_Programming