Tried to open my saved file, then error message appears

— Minecraft Crash Report ----
// Oops.

Time: 11/10/13 4:26 PM
Description: Invalid Biome id

java.lang.NullPointerException: Invalid Biome id
at agn.a(SourceFile:82)
at agl.<init>(SourceFile:26)
at agk.a(SourceFile:52)
at agk.b(SourceFile:61)
at agn.a(SourceFile:61)
at aoj.a(SourceFile:933)
at afn.a(SourceFile:116)
at afn.a(SourceFile:1047)
at bll.i(SourceFile:1328)
at bll.a(SourceFile:919)
at bll.b(SourceFile:813)
at azd.ad(SourceFile:780)
at azd.e(SourceFile:704)
at net.minecraft.client.main.Main.main(SourceFile:103)

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

– Head –
Stacktrace:
at agn.a(SourceFile:82)

– DownfallBlock –
Details:
biome id: 0
downfalls[] size: 256
x: 0
z: 0
w: 16
h: 16
Stacktrace:
at agn.a(SourceFile:82)
at agl.<init>(SourceFile:26)
at agk.a(SourceFile:52)
at agk.b(SourceFile:61)
at agn.a(SourceFile:61)
at aoj.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 afn.a(SourceFile:116)
at afn.a(SourceFile:1047)
at bll.i(SourceFile:1328)
at bll.a(SourceFile:919)

– Affected level –
Details:
Level name: MpServer
All players: 1 total; [bje['zcrox69'/140, 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: (136,64,256), Chunk: (at 8,4,0 in 8,16; contains blocks 128,0,256 to 143,255,271), 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; [bje['zcrox69'/140, 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 biz.a(SourceFile:284)
at azd.b(SourceFile:1951)
at azd.e(SourceFile:713)
at net.minecraft.client.main.Main.main(SourceFile:103)

– System Details –
Details:
Minecraft Version: 1.7.2
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_40, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 273147904 bytes (260 MB) / 370147328 bytes (353 MB) up to 954728448 bytes (910 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
AABB Pool Size: 10003 (560168 bytes; 0 MB) allocated, 10003 (560168 bytes; 0 MB) used
IntCache: cache: 0, tcache: 26, allocated: 12, tallocated: 84
Launched Version: 1.7.2
LWJGL: 2.9.0
OpenGL: GeForce GTX 670/PCIe/SSE2 GL version 4.4.0, NVIDIA Corporation
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: 16 (896 bytes; 0 MB) allocated, 16 (896 bytes; 0 MB) used
Anisotropic Filtering: Off (1)