I loaded the world yesterday on that snapshot and that worked, but now after a long time playing, it has crashed.

Here is the crash the launcher gave me.

---- Minecraft Crash Report ----
// Who set us up the TNT?

Time: 10/07/14 12:32
Description: Exception ticking world

java.lang.IllegalArgumentException: Cannot get property bcl

as it does not exist!
at bbw.b(SourceFile:91)
at ayt.b(SourceFile:127)
at ayt.c(SourceFile:69)
at ary.b(SourceFile:416)
at qg.h(SourceFile:373)
at qg.c(SourceFile:199)
at net.minecraft.server.MinecraftServer.x(SourceFile:578)
at net.minecraft.server.MinecraftServer.w(SourceFile:510)
at cwg.w(SourceFile:132)
at net.minecraft.server.MinecraftServer.run(SourceFile:426)
at java.lang.Thread.run(Unknown Source)

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

– Head –
Stacktrace:
at bbw.b(SourceFile:91)
at ayt.b(SourceFile:127)
at ayt.c(SourceFile:69)
at ary.b(SourceFile:416)
at qg.h(SourceFile:373)
at qg.c(SourceFile:199)

– Affected level –
Details:
Level name: Survival
All players: 1 total; [qj['lAngelP'/234, l='Survival', x=-45,80, y=69,00, z=981,05]]
Chunk stats: ServerChunkCache: 1813 Drop: 0
Level seed: 1954526548411
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options:
Level spawn location: -228,00,64,00,256,00 - World: (-228,64,256), Chunk: (at 12,4,0 in -15,16; contains blocks -240,0,256 to -225,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 2057151 game time, 768406 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 56044 (now: false), thunder time: 152545 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
at net.minecraft.server.MinecraftServer.x(SourceFile:578)
at net.minecraft.server.MinecraftServer.w(SourceFile:510)
at cwg.w(SourceFile:132)
at net.minecraft.server.MinecraftServer.run(SourceFile:426)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 14w28a
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 285854808 bytes (272 MB) / 642252800 bytes (612 MB) up to 954728448 bytes (910 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
Profiler Position: N/A (disabled)
Player Count: 1 / 8; [qj['lAngelP'/234, l='Survival', x=-45,80, y=69,00, z=981,05]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.