noclassdeffound crash when rendering crystal caves

[otakup0pe]

java.lang.NoClassDefFoundError: net/minecraft/world/World$2
	at net.minecraft.world.World.func_190524_a(World.java:557)
	at net.minecraft.world.World.func_175685_c(World.java:495)
	at net.minecraft.world.World.func_175722_b(World.java:440)
	at net.minecraft.world.World.markAndNotifyBlock(World.java:381)
	at net.minecraft.world.World.func_180501_a(World.java:361)
	at net.minecraft.world.World.func_175698_g(World.java:398)
	at vazkii.quark.world.world.CrystalCaveGenerator.hollowOut(CrystalCaveGenerator.java:105)
	at vazkii.quark.world.world.CrystalCaveGenerator.makeCrystalCaveAt(CrystalCaveGenerator.java:77)
	at vazkii.quark.world.world.CrystalCaveGenerator.generate(CrystalCaveGenerator.java:43)
	at net.minecraftforge.fml.common.registry.GameRegistry.generateWorld(GameRegistry.java:167)
	at net.minecraft.world.chunk.Chunk.func_186034_a(Chunk.java:1020)
	at net.minecraft.world.chunk.Chunk.func_186030_a(Chunk.java:999)
	at net.minecraft.world.gen.ChunkProviderServer.func_186025_d(ChunkProviderServer.java:157)
	at net.minecraft.server.management.PlayerChunkMapEntry.func_187268_a(PlayerChunkMapEntry.java:126)
	at net.minecraft.server.management.PlayerChunkMap.func_72693_b(SourceFile:147)
	at net.minecraft.world.WorldServer.func_72835_b(WorldServer.java:227)
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:756)
	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
	at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:185)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
	at java.lang.Thread.run(Unknown Source)

oddly it seems to be happening more since i turned the caves down a bit