Minecraft Crashes when spawning certain mobs (Mac Mountain Lion)

My Crash Log:

--- BEGIN ERROR REPORT aff5246f --------
Generated 10/28/12 8:56 AM

- Minecraft Version: 1.4.2
- Operating System: Mac OS X (x86_64) version 10.8
- Java Version: 1.6.0_33, Apple Inc.
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Apple Inc.
- Memory: 318335896 bytes (303 MB) / 581435392 bytes (554 MB) up to 1065025536 bytes (1015 MB)
- JVM Flags: 3 total; -Xbootclasspath/a:/System/Library/PrivateFrameworks/JavaApplicationLauncher.framework/Resources/LauncherSupport.jar -Xms512M -Xmx1024M
- AABB Pool Size: 2632 (147392 bytes; 0 MB) allocated, 10 (560 bytes; 0 MB) used
- Is Modded: Probably not
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 178 (9968 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
- Player Count: 1 / 8; [ih['HSTSammer'/142, l='The Pretty Scary Update', x=39.06, y=62.66, z=56.99]]
- World The Pretty Scary Update Entities: 0 total; []
- World The Pretty Scary Update Players: 0 total; []
- World The Pretty Scary Update Chunk Stats: ServerChunkCache: 0 Drop: 0
- Type: Integrated Server

java.lang.NoClassDefFoundError: Could not initialize class ns
	at nr.<init>(SourceFile:44)
	at nr.<init>(SourceFile:36)
	at nr.<init>(SourceFile:32)
	at pw.<init>(SourceFile:51)
	at py.bD(SourceFile:162)
	at xr.a(SourceFile:162)
	at xr.a(SourceFile:139)
	at ie.b(SourceFile:106)
	at net.minecraft.server.MinecraftServer.r(SourceFile:717)
	at net.minecraft.server.MinecraftServer.q(SourceFile:661)
	at bcb.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:595)
	at fp.run(SourceFile:818)
--- END ERROR REPORT fead19c7 ----------

Can someone explain what the 'ns' class is.

I was playing around with the new features and it came apparent that, under any difficulty; Zombies, skeletons, creepers, Zombie Pigmen, Witches, Ocelots, and Wolfs will not spawn from mob eggs and in the dark. After about 10-15 seconds after attempting to spawn these mobs the game crashes

**UPDATE!!!**

Ok, so I have updated my Java, and minecraft no longer crashes once spawning these mobs, however they still do not spawn, please see the video in the comments for a demonstration. Thanks