java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
        at java.util.HashMap$ValueIterator.next(Unknown Source)
        at vy.a(Chunk.java:813)
        at rv.a(World.java:2869)
        at wt.a(NetClientHandler.java:420)
        at rk.a(SourceFile:81)
        at iq.b(SourceFile:272)
        at wt.b(NetClientHandler.java:64)
        at gx.c(SourceFile:57)
        at net.minecraft.client.Minecraft.k(SourceFile:1388)
        at net.minecraft.client.Minecraft.run(SourceFile:666)
        at java.lang.Thread.run(Unknown Source)