my worlds will not open from the new version: 1.4.4

Minecraft Crash Report ----
// Ouch. That hurt 😞

Time: 15/11/12 16:48
Description: Exception in server tick loop

java.lang.NullPointerException
at cf.b(SourceFile:103)
at cf.a(SourceFile:35)
at iv.b(SourceFile:437)
at gm.a(SourceFile:72)
at bdr.b(SourceFile:73)
at net.minecraft.server.MinecraftServer.r(SourceFile:769)
at net.minecraft.server.MinecraftServer.q(SourceFile:686)
at bdo.q(SourceFile:117)
at net.minecraft.server.MinecraftServer.run(SourceFile:620)
at fy.run(SourceFile:856)

A detailed walkthrough of the error, its code path and all known details is as follows:
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– System Details –
Details:
Minecraft Version: 1.4.4
Operating System: Windows 7 (amd64) version 6.1
Java Version: 1.6.0_31, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Sun Microsystems Inc.
Memory: 336657384 bytes (321 MB) / 939786240 bytes (896 MB) up to 954466304 bytes (910 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 213389 (11949784 bytes; 11 MB) allocated, 213389 (11949784 bytes; 11 MB) used
Suspicious classes: No suspicious classes found.
IntCache: cache: 0, tcache: 0, allocated: 1, tallocated: 63
Profiler Position: N/A (disabled)
Vec3 Pool Size: 21884 (1225504 bytes; 1 MB) allocated, 21884 (1225504 bytes; 1 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.