My minecraft single player won't open and says that minecraft has crashed.

When I click on my single player world, it comes up with this:

Minecraft has crashed!      
      ----------------------      

Minecraft has stopped running because it encountered a problem; Exception in server tick loop
This error has been saved to C:\Documents and Settings\Alaister\Application Data\.minecraft\crash-reports\crash-2012-11-01_22.21.53-server.txt for your convenience. Please include a copy of this file if you report this crash to anyone.



--- BEGIN ERROR REPORT ea81397b --------
Generated 11/1/12 10:22 PM

- Minecraft Version: 1.4.2
- Operating System: Windows XP (x86) version 5.1
- Java Version: 1.7.0_07, Oracle Corporation
- Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
- Memory: 372018952 bytes (354 MB) / 519110656 bytes (495 MB) up to 1037959168 bytes (989 MB)
- JVM Flags: 2 total; -Xms512m -Xmx1024m
- AABB Pool Size: 542 (30352 bytes; 0 MB) allocated, 542 (30352 bytes; 0 MB) used
- Is Modded: Very likely
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 47 (2632 bytes; 0 MB) allocated, 47 (2632 bytes; 0 MB) used
- Player Count: 0 / 8; []
- World World 2 Entities: 0 total; []
- World World 2 Players: 0 total; []
- World World 2 Chunk Stats: ServerChunkCache: 0 Drop: 0
- Type: Integrated Server

java.lang.VerifyError: (class: com/sijobe/spc/wrapper/Minecraft, method: getPlayer signature: ()Lcom/sijobe/spc/wrapper/Player;) Incompatible argument to function
	at com.sijobe.spc.core.Constants.<clinit>(Constants.java:35)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Unknown Source)
	at ih.<clinit>(ih.java:741)
	at ge.a(SourceFile:216)
	at bce.b(SourceFile:66)
	at net.minecraft.server.MinecraftServer.r(SourceFile:731)
	at net.minecraft.server.MinecraftServer.q(SourceFile:661)
	at bcb.q(SourceFile:117)
	at net.minecraft.server.MinecraftServer.run(SourceFile:595)
	at fp.run(SourceFile:818)
--- END ERROR REPORT 325ce51c ----------

To trigger this you:

1. Open Minecraft
2. Try to Open your single player world
3. The screen will then freeze on the main menu and then show you the report above.