Custom World glitch?

[09:45:01] [Client thread/INFO]: Setting user: Skullkillington
[09:45:01] [Client thread/INFO]: (Session ID is token:0588a34ae6634d68aeb958f8c0f293b2:a0c0ce70bb2a424397468a337997db94)
[09:45:03] [Client thread/INFO]: LWJGL Version: 2.9.1
[09:45:04] [Client thread/INFO]: Reloading ResourceManager: Default

Starting up SoundSystem...
Initializing LWJGL OpenAL
    (The LWJGL binding of OpenAL.  For more information, see http://www.lwjgl.org)
OpenAL initialized.

[09:45:06] [Sound Library Loader/INFO]: Sound engine started
[09:45:07] [Client thread/WARN]: File minecraft:sounds/mob/ghast/fireball.ogg does not exist, cannot add it to event minecraft:item.fireCharge.use
[09:45:17] [Client thread/INFO]: Created: 512x512 textures-atlas
[09:50:35] [Server thread/INFO]: Starting integrated minecraft server version 14w31a
[09:50:35] [Server thread/INFO]: Generating keypair
[09:50:35] [Server thread/INFO]: Converting map!
[09:50:35] [Server thread/INFO]: Scanning folders...
[09:50:35] [Server thread/INFO]: Total conversion count is 0
[09:50:36] [Server thread/INFO]: Preparing start region for level 0
[09:50:36] [Server thread/ERROR]: Encountered an unexpected exception
java.lang.IllegalArgumentException: n must be positive
	at java.util.Random.nextInt(Unknown Source) ~[?:1.7.0_65]
	at arl.b(SourceFile:281) ~[14w31a.jar:?]
	at arl.a(SourceFile:297) ~[14w31a.jar:?]
	at arl.a(SourceFile:92) ~[14w31a.jar:?]
	at arl.a(SourceFile:49) ~[14w31a.jar:?]
	at aqz.a(SourceFile:388) ~[14w31a.jar:?]
	at asa.a(SourceFile:85) ~[14w31a.jar:?]
	at bfx.a(SourceFile:472) ~[14w31a.jar:?]
	at qn.a(SourceFile:174) ~[14w31a.jar:?]
	at bek.a(SourceFile:858) ~[14w31a.jar:?]
	at qn.c(SourceFile:104) ~[14w31a.jar:?]
	at net.minecraft.server.MinecraftServer.j(SourceFile:314) ~[14w31a.jar:?]
	at cxc.a(SourceFile:111) ~[14w31a.jar:?]
	at cxc.h(SourceFile:127) ~[14w31a.jar:?]
	at net.minecraft.server.MinecraftServer.run(SourceFile:416) [14w31a.jar:?]
	at java.lang.Thread.run(Unknown Source) [?:1.7.0_65]
[09:50:36] [Server thread/ERROR]: This crash report has been saved to: C:\Users\Owner\AppData\Roaming\.minecraft\crash-reports\crash-2014-08-02_09.50.36-server.txt
[09:50:36] [Server thread/INFO]: Stopping server
[09:50:36] [Server thread/INFO]: Saving players
[09:50:36] [Server thread/INFO]: Saving worlds
[09:50:36] [Server thread/INFO]: Saving chunks for level 'New World'/Overworld
[09:50:36] [Server thread/INFO]: Saving chunks for level 'New World'/Nether
[09:50:36] [Server thread/INFO]: Saving chunks for level 'New World'/The End