Cuando pongo el mod mo´creatures me aparece esto:

—- Minecraft Crash Report —-
// Hey, that tickles! Hehehe!

Time: 24/01/14 15:01
Description: Ticking entity

java.lang.NoClassDefFoundError: net/minecraftforge/event/world/BlockEvent$BreakEvent
at drzhark.mocreatures.MoCTools.destroyRandomBlockWithMetadata(MoCTools.java:1207)
at drzhark.mocreatures.entity.monster.MoCEntityMiniGolem.acquireTRock(MoCEntityMiniGolem.java:105)
at drzhark.mocreatures.entity.monster.MoCEntityMiniGolem.func_70636_d(MoCEntityMiniGolem.java:92)
at net.minecraft.entity.EntityLivingBase.func_70071_h_(EntityLivingBase.java:1826)
at net.minecraft.entity.EntityLiving.func_70071_h_(EntityLiving.java:257)
at net.minecraft.entity.monster.EntityMob.func_70071_h_(SourceFile:29)
at net.minecraft.world.World.func_72866_a(World.java:2350)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:721)
at net.minecraft.world.World.func_72870_g(World.java:2311)
at net.minecraft.world.World.func_72939_s(World.java:2157)
at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:552)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:666)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:585)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:175)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:482)
at net.minecraft.server.ThreadMinecraftServer.run(SourceFile:582)
Caused by: java.lang.ClassNotFoundException: net.minecraftforge.event.world.BlockEvent$BreakEvent
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:179)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
… 16 more
Caused by: java.lang.NullPointerException
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:171)
… 18 more

A detailed walkthrough of the error, its code path and all known details is as follows:
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— Head —
Stacktrace:
at drzhark.mocreatures.MoCTools.destroyRandomBlockWithMetadata(MoCTools.java:1207)
at drzhark.mocreatures.entity.monster.MoCEntityMiniGolem.acquireTRock(MoCEntityMiniGolem.java:105)
at drzhark.mocreatures.entity.monster.MoCEntityMiniGolem.func_70636_d(MoCEntityMiniGolem.java:92)
at net.minecraft.entity.EntityLivingBase.func_70071_h_(EntityLivingBase.java:1826)
at net.minecraft.entity.EntityLiving.func_70071_h_(EntityLiving.java:257)
at net.minecraft.entity.monster.EntityMob.func_70071_h_(SourceFile:29)
at net.minecraft.world.World.func_72866_a(World.java:2350)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:721)
at net.minecraft.world.World.func_72870_g(World.java:2311)