I've run into this error in mine when I added it to my DW 20 pack.
@Reika directed me here.
java.lang.ClassCastException: Reika.RotaryCraft.Entities.EntityFreezeGunShot cannot be cast to net.minecraft.entity.EntityLivingBase
at net.minecraft.network.play.server.S0FPacketSpawnMob.func_148833_a(SourceFile:97)
at net.minecraft.client.multiplayer.GuiConnecting.func_73876_c(SourceFile:78)
Is the error I got.
My client launches fine, but crashes once I try to connect to the server. When I first launched the server, I was able to connect fine, this just transpired over time.
Any thoughts guys?