Hopper: java.lang.NoClassDefFoundError: com/mojang/authlib/yggdrasil/YggdrasilAuthenticationService

This is an automatically generated report based from the following crash: http://hopper.minecraft.net/crashes/minecraft/MCX-465320/

Crash:

java.lang.NoClassDefFoundError: com/mojang/authlib/yggdrasil/YggdrasilAuthenticationService
	at net.minecraft.server.MinecraftServer.<init>(SourceFile:117)
	at bsk.<init>(SourceFile:38)

The following is the first clean report made public about this crash:

---- Minecraft Crash Report ----
// I feel sad now :(

Time: 10/25/13 8:43 AM
Description: Starting integrated server

java.lang.NoClassDefFoundError: com/mojang/authlib/yggdrasil/YggdrasilAuthenticationService
	at net.minecraft.server.MinecraftServer.<init>(SourceFile:117)
	at bsk.<init>(SourceFile:38)
	at azd.a(SourceFile:1591)
	at bbi.a(SourceFile:202)
	at bbi.a(SourceFile:292)
	at bcd.l(SourceFile:258)
	at bcd.k(SourceFile:217)
	at azd.o(SourceFile:1303)
	at azd.ad(SourceFile:753)
	at azd.e(SourceFile:704)
	at net.minecraft.client.main.Main.main(SourceFile:103)
Caused by: java.lang.ClassNotFoundException: com.mojang.authlib.yggdrasil.YggdrasilAuthenticationService
	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)
	... 11 more


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at net.minecraft.server.MinecraftServer.<init>(SourceFile:117)
	at bsk.<init>(SourceFile:38)

-- Starting integrated server --
Details:
	Level ID: 1_7_2
	Level Name: 1.7.2
Stacktrace:
	at azd.a(SourceFile:1591)
	at bbi.a(SourceFile:202)
	at bbi.a(SourceFile:292)
	at bcd.l(SourceFile:258)
	at bcd.k(SourceFile:217)

-- Affected screen --
Details:
	Screen name: btj
Stacktrace:
	at azd.o(SourceFile:1303)
	at azd.ad(SourceFile:753)
	at azd.e(SourceFile:704)
	at net.minecraft.client.main.Main.main(SourceFile:103)

-- System Details --
Details:
	Minecraft Version: 1.7.2
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_06, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 205689560 bytes (196 MB) / 244187136 bytes (232 MB) up to 954466304 bytes (910 MB)
	JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	Launched Version: 1.7.2
	LWJGL: 2.9.0
	OpenGL: GeForce GTX 560 SE/PCIe/SSE2 GL version 4.4.0, NVIDIA Corporation
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: []
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null
	Anisotropic Filtering: Off (1)

You can see this full report at http://hopper.minecraft.net/crashes/minecraft/MCX-465320/21348335/