I've been playing on my singleplayer world for a month now (Made it Aug 1, for Minecraft 1.3.1). I have not had any prior trouble with it.
I logged on earlier today inside a block. I got out, did a bunch of stuff, then Minecraft crashed. I logged back in and everything I did was set back and I was inside the block again. Minecraft crashed again. Now, whenever I open that world, it says "Building Terrain", takes me back to the start screen, and crashes sometime later. All of my other worlds are currently working.
Yes, I'm not sure where to access the logs so I will duplicate it and tell you post it:
The mods that I have installed are Optifine and Togglesneak; both of which I have had for a while without previous problems.
Minecraft has crashed!
Minecraft has stopped running because it encountered a problem; Exception in server tick loop
This error has been saved to C:\Users\Brian\AppData\Roaming\.minecraft\crash-reports\crash-2012-09-01_22.26.43-server.txt for your convenience. Please include a copy of this file if you report this crash to anyone.
--- BEGIN ERROR REPORT b020ee53 --------
Generated 9/1/12 10:26 PM
- Minecraft Version: 1.3.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.6.0_27, Sun Microsystems Inc.
- Java VM Version: Java HotSpot™ 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
- Memory: 328965416 bytes (313 MB) / 585826304 bytes (558 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xms512m -Xmx1024m
- Is Modded: Very likely
- Profiler Position: N/A (disabled)
- Player Count: 0 / 8; 
- World 1.3 Survival Entities: 0 total; 
- World 1.3 Survival Players: 0 total; 
- World 1.3 Survival Chunk Stats: ServerChunkCache: 0 Drop: 0
- Type: Integrated Server
--- END ERROR REPORT f5cad15 ----------