Hello,

As reported on bukkit forums. Oddly for me I do not recieve this error on my Windows 7 test server, however it appears on my CentOS 5 server. The plugin however runs as expected (not tested creature spawn protection however).

Current Bukkit: This server is running Craftbukkit version git-Bukkit-0.0.0-706-gf53e007-b740jnks (MC: 1.5_02)

WorldGuard: WorldGuard 5.0-alpha10

Other plugins: Minequery
LWC
Permissions
LocalShops
mcMMO
NETHRAR
SpawnMob
BorderGuard
OddItem
Towny
SpawnX
Dynmap
WorldEdit
AutoSave
iConomy
BBROTHER
Prefixer
SimpleWhisper
nSpleef
Warpz0r
motd
cjb_mod_manager
AssignPermissions
Stats-0.985
Achievements-0.981
CookieMonster
HeroicDeath
Money2XP
ChocolateFever
Tele++
OddGive

[SEVERE] Could not pass event CREATURE_SPAWN to WorldGuard
java.lang.NullPointerException
at com.sk89q.worldguard.bukkit.WorldGuardEntityListener.onCreatureSpawn(WorldGuardEntityListener.java:397)
at org.bukkit.plugin.java.JavaPluginLoader$51.execute(JavaPluginLoader.java:516)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:59)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:257)
at org.bukkit.craftbukkit.event.CraftEventFactory.callCreatureSpawnEvent(CraftEventFactory.java:228)
at net.minecraft.server.World.a(World.java:1790)
at net.minecraft.server.Chunk.addEntities(Chunk.java:470)
at net.minecraft.server.ChunkProviderServer.getChunkAt(ChunkProviderServer.java:75)
at org.bukkit.craftbukkit.CraftServer.createWorld(CraftServer.java:344)
at org.bukkit.craftbukkit.CraftServer.createWorld(CraftServer.java:296)
at org.akrieger.Nethrar.Nethrar.onEnable(Nethrar.java:83)
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:127)
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:632)
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:218)
at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:116)
at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:94)
at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:217)
at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:204)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:144)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:259)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:394)

#80
I'll just leave this here
Also this: http://redmine.sk89q.com/issues/439