World Creation Issue

---- Minecraft Crash Report ----
// Surprise! Haha. Well, this is awkward.

Time: 6/1/13 4:42 AM
Description: Exception in server tick loop

java.lang.NoClassDefFoundError: com/google/gson/GsonBuilder
	at cp.<clinit>(SourceFile:12)
	at gz.a(SourceFile:81)
	at bik.b(SourceFile:73)
	at net.minecraft.server.MinecraftServer.s(SourceFile:491)
	at net.minecraft.server.MinecraftServer.r(SourceFile:408)
	at bih.r(SourceFile:125)
	at net.minecraft.server.MinecraftServer.run(SourceFile:342)
	at gu.run(SourceFile:585)
Caused by: java.lang.ClassNotFoundException: com.google.gson.GsonBuilder
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	... 8 more


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: 13w22a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_13, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 118096608 bytes (112 MB) / 388825088 bytes (370 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 1 total; -Xmx1G
	AABB Pool Size: 257 (14392 bytes; 0 MB) allocated, 243 (13608 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: 37 (2072 bytes; 0 MB) allocated, 37 (2072 bytes; 0 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.