go into .minecraft/versions or bin/ delete your profile or minecraft.jar

I meant, does Java interpret the lack of META-INF as the presence of a mod?

I don't have the META-INF file. Does that count as 'modded'?

I removed the remnants from World Edit from Minecraft.jar. It still doesn't work? And the report still says I have mods:
---- Minecraft Crash Report ----
// Oh - I know what I did wrong!

Time: 20/12/13 13:48
Description: Reading NBT data

java.lang.ClassCastException: bz cannot be cast to cb
at bs.f(SourceFile:134)
at ace.a(SourceFile:30)
at ajq.a(SourceFile:215)
at ajq.a(SourceFile:186)
at ajq.a(SourceFile:145)
at net.minecraft.server.MinecraftServer.b(SourceFile:112)
at bjg.a(SourceFile:59)
at bjg.c(SourceFile:104)
at net.minecraft.server.MinecraftServer.run(SourceFile:306)
at gp.run(SourceFile:573)


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

-- Corrupt NBT tag --
Details:
Tag type found: INT
Tag type expected: LONG
Tag name: LastUpdate
Tag parent: Level
Stacktrace:
at bs.f(SourceFile:134)
at ace.a(SourceFile:30)
at ajq.a(SourceFile:215)
at ajq.a(SourceFile:186)
at ajq.a(SourceFile:145)
at net.minecraft.server.MinecraftServer.b(SourceFile:112)
at bjg.a(SourceFile:59)
at bjg.c(SourceFile:104)
at net.minecraft.server.MinecraftServer.run(SourceFile:306)
at gp.run(SourceFile:573)

-- System Details --
Details:
Minecraft Version: 1.5.2
Operating System: Windows NT (unknown) (x86) version 6.2
Java Version: 1.6.0_27, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Sun Microsystems Inc.
Memory: 45095736 bytes (43 MB) / 85147648 bytes (81 MB) up to 259522560 bytes (247 MB)
JVM Flags: 0 total;
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Profiler Position: N/A (disabled)
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Very likely; Jar signature invalidated

quote fail

[/quote]
I have none[/quote]
You have mods. The crash report says so.[/quote]

I tried installing World Edit once, but I did something wrong. Maybe that's it?[/quote]

uninstall it then

samtyler654I downloaded a map that had to be converted. People said on the internet that to convert a map you just have to click on it and the game will convert it. When I click on it, a screen saying 'Converting World' comes up, but nothing happens. I tried doing that 3 or 4 times but it never works. Do I have to convert it manually? Does minimising Minecraft stop the process?

I started a Survival world in Beta 1.7, just for fun, and when I was bored, I played it on 1.7.2. It said me "Converting world" too. I just waited a little, and the world was loaded with the biomes form, my house, and all the things I had there.

Do you have any mods running? Even Optifine could effect it...

---- Minecraft Crash Report ----
// I blame Dinnerbone.

Time: 20/12/13 13:06
Description: Reading NBT data

java.lang.ClassCastException: bz cannot be cast to cb
at bs.f(SourceFile:134)
at ace.a(SourceFile:30)
at ajq.a(SourceFile:215)
at ajq.a(SourceFile:186)
at ajq.a(SourceFile:145)
at net.minecraft.server.MinecraftServer.b(SourceFile:112)
at bjg.a(SourceFile:59)
at bjg.c(SourceFile:104)
at net.minecraft.server.MinecraftServer.run(SourceFile:306)
at gp.run(SourceFile:573)


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

-- Corrupt NBT tag --
Details:
Tag type found: INT
Tag type expected: LONG
Tag name: LastUpdate
Tag parent: Level
Stacktrace:
at bs.f(SourceFile:134)
at ace.a(SourceFile:30)
at ajq.a(SourceFile:215)
at ajq.a(SourceFile:186)
at ajq.a(SourceFile:145)
at net.minecraft.server.MinecraftServer.b(SourceFile:112)
at bjg.a(SourceFile:59)
at bjg.c(SourceFile:104)
at net.minecraft.server.MinecraftServer.run(SourceFile:306)
at gp.run(SourceFile:573)

-- System Details --
Details:
Minecraft Version: 1.5.2
Operating System: Windows NT (unknown) (x86) version 6.2
Java Version: 1.6.0_27, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Sun Microsystems Inc.
Memory: 40207960 bytes (38 MB) / 79536128 bytes (75 MB) up to 259522560 bytes (247 MB)
JVM Flags: 0 total;
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Profiler Position: N/A (disabled)
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Very likely; Jar signature invalidated

Go to %appdata%, crash logs. Delete all the crash logs, boot the game again, go into the world, and there should be created a new crash log. Show the text inside to me, so I can understand the crash better.

No, nothing happens, just the screen. When I try to close Minecraft when the screen is showing, though, it crashes and I have to press Ctrl + Alt + Del. I'm using 1.5.2.

Hmm, do you get a crash report? What version are you using? 1.6+?

No, it is a Top Gear Track map

What world is it? "It's better together"? Is it this map? If it is, just tell me. Becuse that map has a corrupted NBT-Tag.