20:49:26 [SEVERE] net.minecraft.util.ReportedException: Ticking entity
20:49:26 [SEVERE]       at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:896)
20:49:26 [SEVERE]       at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:323)
20:49:26 [SEVERE]       at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:786)
20:49:26 [SEVERE]       at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:670)
20:49:26 [SEVERE]       at net.minecraft.server.ThreadMinecraftServer.run(Unknown Source)
20:49:26 [SEVERE] Caused by: java.util.ConcurrentModificationException
20:49:26 [SEVERE]       at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
20:49:26 [SEVERE]       at java.util.HashMap$KeyIterator.next(Unknown Source)
20:49:26 [SEVERE]       at net.minecraft.entity.EntityLiving.func_70679_bo(EntityLiving.java:2473)
20:49:26 [SEVERE]       at net.minecraft.entity.EntityLiving.func_70030_z(EntityLiving.java:676)
20:49:26 [SEVERE]       at net.minecraft.entity.Entity.func_70071_h_(Entity.java:473)
20:49:26 [SEVERE]       at net.minecraft.entity.EntityLiving.func_70071_h_(EntityLiving.java:827)
20:49:26 [SEVERE]       at net.minecraft.entity.monster.EntityMob.func_70071_h_(EntityMob.java:46)
20:49:26 [SEVERE]       at net.minecraft.entity.monster.EntityZombie.func_70071_h_(EntityZombie.java:215)
20:49:26 [SEVERE]       at net.minecraft.world.World.func_72866_a(World.java:2426)
20:49:26 [SEVERE]       at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:958)
20:49:26 [SEVERE]       at net.minecraft.world.World.func_72870_g(World.java:2379)
20:49:26 [SEVERE]       at net.minecraft.world.World.func_72939_s(World.java:2191)
20:49:26 [SEVERE]       at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:777)
20:49:26 [SEVERE]       at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:890)
20:49:26 [SEVERE]       ... 4 more
20:49:26 [SEVERE] Encountered an unexpected exception ReportedException
net.minecraft.util.ReportedException: Ticking entity
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:896)
        at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:323)
        at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:786)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:670)
        at net.minecraft.server.ThreadMinecraftServer.run(Unknown Source)
Caused by: java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
        at java.util.HashMap$KeyIterator.next(Unknown Source)
        at net.minecraft.entity.EntityLiving.func_70679_bo(EntityLiving.java:2473)
        at net.minecraft.entity.EntityLiving.func_70030_z(EntityLiving.java:676)
        at net.minecraft.entity.Entity.func_70071_h_(Entity.java:473)
        at net.minecraft.entity.EntityLiving.func_70071_h_(EntityLiving.java:827)
        at net.minecraft.entity.monster.EntityMob.func_70071_h_(EntityMob.java:46)
        at net.minecraft.entity.monster.EntityZombie.func_70071_h_(EntityZombie.java:215)
        at net.minecraft.world.World.func_72866_a(World.java:2426)
        at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:958)
        at net.minecraft.world.World.func_72870_g(World.java:2379)
        at net.minecraft.world.World.func_72939_s(World.java:2191)
        at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:777)
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:890)
        ... 4 more