Aether mod error with loading world

I recently installed the aether mod, and everything was working fine until I tried to load my world - minecraft crashed. the same error was given when creating a new world. Here's the report -

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

Minecraft has stopped running because it encountered a problem; Updating screen events

A full error report has been saved to C:\Users\eoin9_000\AppData\Roaming\.minecraft\crash-reports\crash-2013-02-16_11.17.23-client.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash



--- BEGIN ERROR REPORT 79f6705e --------
Full report at:
C:\Users\eoin9_000\AppData\Roaming\.minecraft\crash-reports\crash-2013-02-16_11.17.23-client.txt
Please show that file to Mojang, NOT just this screen!

Generated 16/02/13 11:17

-- Head --
Stacktrace:
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
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 java.lang.ClassLoader.loadClass(Unknown Source)
at net.minecraft.server.MinecraftServer.al(SourceFile:330)
at net.minecraft.server.MinecraftServer.<init>(SourceFile:104)
at bdz.<init>(SourceFile:32)
at net.minecraft.client.Minecraft.a(SourceFile:1385)
at auo.e(SourceFile:157)
at auo.a(SourceFile:122)
at aul.a(SourceFile:72)
at aul.d(SourceFile:127)
at aul.m(SourceFile:111)

-- Affected screen --
Details:
Screen name: bey
Stacktrace:
at net.minecraft.client.Minecraft.l(SourceFile:1086)
at net.minecraft.client.Minecraft.J(SourceFile:582)
at net.minecraft.client.Minecraft.run(SourceFile:534)
at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
Minecraft Version: 1.4.7
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_11, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 477174624 bytes (455 MB) / 519110656 bytes (495 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 2 total; -Xms512m -Xmx1024m
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Suspicious classes: GuiAchievementAether]
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
LWJGL: 2.4.2
OpenGL: Intel(R) HD Graphics 4000 GL version 4.0.0 - Build 9.17.10.2828, Intel
Is Modded: Very likely; Jar signature invalidated
Type: Client (map_client.txt)
Texture Pack: Default
Profiler Position: N/A (disabled)
Vec3 Pool Size: ~~ERROR~~ NullPointerException: null

java.lang.VerifyError: Cannot inherit from final class
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
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 java.lang.ClassLoader.loadClass(Unknown Source)
at net.minecraft.server.MinecraftServer.al(SourceFile:330)
at net.minecraft.server.MinecraftServer.<init>(SourceFile:104)
at bdz.<init>(SourceFile:32)
at net.minecraft.client.Minecraft.a(SourceFile:1385)
at auo.e(SourceFile:157)
at auo.a(SourceFile:122)
at aul.a(SourceFile:72)
at aul.d(SourceFile:127)
at aul.m(SourceFile:111)
at net.minecraft.client.Minecraft.l(SourceFile:1086)
at net.minecraft.client.Minecraft.J(SourceFile:582)
at net.minecraft.client.Minecraft.run(SourceFile:534)
at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 9d09fd02 ----------