After like 5min of gameplay on a server i've played on alot before, i get this message.

This came after the 1.3 update. any ideas?

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

Minecraft has stopped running because it encountered a problem; Unexpected error
This error has been saved to C:\Users\Jens\AppData\Roaming\.minecraft\crash-reports\crash-2012-08-03_20.59.50-client.txt for your convenience. Please include a copy of this file if you report this crash to anyone.

--- BEGIN ERROR REPORT 464c8bbf --------
Generated 03-08-12 20:59

- Minecraft Version: 1.3.1
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.7.0_05, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 446765136 bytes (426 MB) / 514523136 bytes (490 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xms512m -Xmx1024m
- LWJGL: 2.4.2
- OpenGL: GeForce GTX 560/PCIe/SSE2 GL version 4.2.0, NVIDIA Corporation
- Is Modded: Probably not
- Type: Client
- Texture Pack: doku alecs - Remade by Leaske.zip
- Profiler Position: N/A (disabled)

java.lang.NullPointerException
at asu.a(SourceFile:449)
at ee.a(SourceFile:44)
at bb.b(SourceFile:333)
at asu.d(SourceFile:81)
at atc.b(SourceFile:51)
at net.minecraft.client.Minecraft.l(SourceFile:1261)
at net.minecraft.client.Minecraft.J(SourceFile:583)
at net.minecraft.client.Minecraft.run(SourceFile:535)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT fa3ab7cb ----------