Server Crash when joined

[jwh1998]

Well heres my error report if anyone knows what is wrong
---- Minecraft Crash Report ----
// Everything's going to plan. No, really, that was supposed to happen.

Time: 11/20/12 3:36 PM
Description: Exception in server tick loop

java.lang.ArrayIndexOutOfBoundsException: 4
at ln.bB(EntityLiving.java:2595)
at pw.bB(SourceFile:199)
at pw.bD(SourceFile:222)
at xr.a(SpawnerAnimals.java:233)
at xr.a(SpawnerAnimals.java:170)
at ie.b(WorldServer.java:116)
at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:648)
at hg.r(DedicatedServer.java:241)
at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:585)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:492)
at fp.run(SourceFile:818)

Relevant Details:
- Minecraft Version: 1.4.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.7.0_04, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 1313018376 bytes (1252 MB) / 1450770432 bytes (1383 MB) up to 7635533824 bytes (7281 MB)
- JVM Flags: 2 total; -Xms512M -Xmx8G
- AABB Pool Size: 3886 (217616 bytes; 0 MB) allocated, 2 (112 bytes; 0 MB) used
- FML: ~ERROR~ NullPointerException: null
- Is Modded: Definitely; 'forge,fml'
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
- Player Count: 1 / 4; [ih['jwh1998'/22, l='withnik', x=174.39, y=90.29, z=-232.64]]
- World withnik Entities: 0 total; []
- World withnik Players: 0 total; []
- World withnik Chunk Stats: ServerChunkCache: 0 Drop: 0
- Type: Dedicated Server

if this is supposed to happen and im just being stupid let me know thanks.