[Crashing as soon as i join a server]

Hi, as soon as i join a server my game crashes i have tried a lot of the fixes that are on the forums but none work so here is my error log

---- Minecraft Crash Report ----

// Uh... Did I do that?

Time: 31/05/13 5:51 PM

Description: Unexpected error

java.lang.IndexOutOfBoundsException

at com.eloraam.redpower.core.ItemExtended.d(ItemExtended.java:33)

at up.i(Item.java:458)

at up.l(Item.java:600)

at ur.r(SourceFile:334)

at atr.a(GuiIngame.java:406)

at ban.b(EntityRenderer.java:982)

at net.minecraft.client.Minecraft.J(Minecraft.java:884)

at net.minecraft.client.Minecraft.run(Minecraft.java:773)

at java.lang.Thread.run(Unknown Source)

I hope this is enough information to help me

Thanks