Minecraft – Invalid Biome ID

I just loaded my YouTube Minecraft LP world and the game crashed. I had opened the world just yesterday as well! The report looked like this:

---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 1/1/14 8:57 AM
Description: Invalid Biome id

java.lang.NullPointerException: Invalid Biome id
    at ags.a(SourceFile:82)
    at agq.<init>(SourceFile:26)
    at agp.a(SourceFile:52)
    at agp.b(SourceFile:61)
    at ags.a(SourceFile:61)
    at aoo.a(SourceFile:933)
    at afs.a(SourceFile:116)
    at afs.a(SourceFile:1047)
    at bmm.j(SourceFile:1343)
    at bmm.a(SourceFile:928)
    at bmm.b(SourceFile:816)
    at azi.ah(SourceFile:787)
    at azi.f(SourceFile:711)
    at net.minecraft.client.main.Main.main(SourceFile:152)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
    at ags.a(SourceFile:82)

-- DownfallBlock --
Details:
    biome id: 0
    downfalls[] size: 256
    x: 0
    z: 0
    w: 16
    h: 16
Stacktrace:
    at ags.a(SourceFile:82)
    at agq.<init>(SourceFile:26)
    at agp.a(SourceFile:52)
    at agp.b(SourceFile:61)
    at ags.a(SourceFile:61)
    at aoo.a(SourceFile:933)

-- Coordinates of biome request --
Details:
    Location: World: (8,0,8), Chunk: (at 8,0,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Stacktrace:
    at afs.a(SourceFile:116)
    at afs.a(SourceFile:1047)
    at bmm.j(SourceFile:1343)
    at bmm.a(SourceFile:928)

-- Affected level --
Details:
    Level name: MpServer
    All players: 1 total; [bkf['Ethan_Bacon'/224, l='MpServer', x=8.50, y=66.62, z=8.50]]
    Chunk stats: MultiplayerChunkCache: 0, 0
    Level seed: 0
    Level generator: ID 00 - default, ver 1. Features enabled: false
    Level generator options: 
    Level spawn location: World: (163,64,198), Chunk: (at 3,4,6 in 10,12; contains blocks 160,0,192 to 175,255,207), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
    Level time: 0 game time, 0 day time
    Level dimension: 0
    Level storage version: 0x00000 - Unknown?
    Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
    Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
    Forced entities: 1 total; [bkf['Ethan_Bacon'/224, l='MpServer', x=8.50, y=66.62, z=8.50]]
    Retry entities: 0 total; []
    Server brand: vanilla
    Server type: Integrated singleplayer server
Stacktrace:
    at bka.a(SourceFile:289)
    at azi.b(SourceFile:1952)
    at azi.f(SourceFile:720)
    at net.minecraft.client.main.Main.main(SourceFile:152)

-- System Details --
Details:
    Minecraft Version: 1.7.4
    Operating System: Windows 8 (amd64) version 6.2
    Java Version: 1.7.0_25, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 268770352 bytes (256 MB) / 373489664 bytes (356 MB) up to 954466304 bytes (910 MB)
    JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
    AABB Pool Size: 17427 (975912 bytes; 0 MB) allocated, 17427 (975912 bytes; 0 MB) used
    IntCache: cache: 0, tcache: 14, allocated: 12, tallocated: 94
    Launched Version: 1.7.4
    LWJGL: 2.9.1
    OpenGL: AMD Radeon HD 7570 GL version 4.2.12002 Compatibility Profile Context 9.12.0.0, ATI Technologies Inc.
    GL Caps: Using GL 1.3 multitexturing.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Anisotropic filtering is supported and maximum anisotropy is 16.
Shaders are available because OpenGL 2.1 is supported.

    Is Modded: Probably not. Jar signature remains and client brand is untouched.
    Type: Client (map_client.txt)
    Resource Packs: []
    Current Language: English (US)
    Profiler Position: N/A (disabled)
    Vec3 Pool Size: 18 (1008 bytes; 0 MB) allocated, 18 (1008 bytes; 0 MB) used
    Anisotropic Filtering: Off (1)

I checked that I had loaded the correct version (1.7.4) and I had. What is going on here?