Bukkit had a boo-boo:
---- Minecraft Crash Report ----
// I just don't know what went wrong
Time: 09/12/12 07:01
Description: Exception in server tick loop
java.lang.NullPointerException
at net.minecraft.server.DedicatedServer.al(DedicatedServer.java:254)
at net.minecraft.server.DedicatedServer.a(DedicatedServer.java:200)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:433)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:856)
Rarely happens, we'll look to updating the latest version a little later.