java.lang.NoClassDefFoundError: codechicken/lib/math/MathHelper
at com.hbm.main.ModEventHandler.onPlayerTick(ModEventHandler.java:1105)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_45_ModEventHandler_onPlayerTick_PlayerTickEvent.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:140)
at cpw.mods.fml.common.FMLCommonHandler.onPlayerPreTick(FMLCommonHandler.java:345)
at net.minecraft.entity.player.EntityPlayer.func_70071_h_(EntityPlayer.java:220)
at net.minecraft.client.entity.EntityClientPlayerMP.func_70071_h_(SourceFile:63)
at net.minecraft.world.World.func_72866_a(World.java:2070)
at net.minecraft.world.World.func_72870_g(World.java:2034)
at net.minecraft.world.World.func_72939_s(World.java:1887)
at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:2006)
at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:973)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:898)
at net.minecraft.client.main.Main.main(SourceFile:148)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
Caused by: java.lang.ClassNotFoundException: codechicken.lib.math.MathHelper
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 20 more
Caused by: java.lang.NullPointerException
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
... 22 more

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

-- Head --
Stacktrace:
at com.hbm.main.ModEventHandler.onPlayerTick(ModEventHandler.java:1105)
at cpw.mods.fml.common.eventhandler.ASMEventHandler_45_ModEventHandler_onPlayerTick_PlayerTickEvent.invoke(.dynamic)
at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54)
at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:140)
at cpw.mods.fml.common.FMLCommonHandler.onPlayerPreTick(FMLCommonHandler.java:345)
at net.minecraft.entity.player.EntityPlayer.func_70071_h_(EntityPlayer.java:220)
at net.minecraft.client.entity.EntityClientPlayerMP.func_70071_h_(SourceFile:63)
at net.minecraft.world.World.func_72866_a(World.java:2070)
at net.minecraft.world.World.func_72870_g(World.java:2034)

-- Entity being ticked --
Details:
Entity Type: null (net.minecraft.client.entity.EntityClientPlayerMP)
Entity ID: 22
Entity Name: LS96
Entity's Exact location: 8.50, 66.62, 8.50
Entity's Block location: World: (8,66,8), Chunk: (at 8,4,8 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: 0.00, 0.00, 0.00
Stacktrace:
at net.minecraft.world.World.func_72939_s(World.java:1887)

-- Affected level --
Details:
Level name: MpServer
All players: 1 total; [EntityClientPlayerMP['LS96'/22, l='MpServer', x=8.50, y=66.62, z=8.50]]
Chunk stats: MultiplayerChunkCache: 0, 0
Level seed: 0
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: World: (-252,64,-160), Chunk: (at 4,4,0 in -16,-10; contains blocks -256,0,-160 to -241,255,-145), Region: (-1,-1; contains chunks -32,-32 to -1,-1, blocks -512,0,-512 to -1,255,-1)
Level time: 1 game time, 1 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: Game mode: creative (ID 1). Hardcore: false. Cheats: false
Forced entities: 1 total; [EntityClientPlayerMP['LS96'/22, l='MpServer', x=8.50, y=66.62, z=8.50]]
Retry entities: 0 total; []
Server brand: fml,forge
Server type: Integrated singleplayer server
Stacktrace:
at net.minecraft.client.multiplayer.WorldClient.func_72914_a(WorldClient.java:373)
at net.minecraft.client.Minecraft.func_71396_d(Minecraft.java:2444)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:919)
at net.minecraft.client.main.Main.main(SourceFile:148)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
Edit
Downlaoding codechickencore fixed it