Error

java.util.ConcurrentModificationException
    at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
    at java.util.HashMap$KeyIterator.next(Unknown Source)
    at java.util.AbstractCollection.toArray(Unknown Source)
    at java.util.ArrayList.<init>(Unknown Source)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.e(BlockRedstoneWire.java:42)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.doPhysics(BlockRedstoneWire.java:237)
    at net.minecraft.server.v1_7_R1.World.e(World.java:486)
    at net.minecraft.server.v1_7_R1.World.applyPhysics(World.java:438)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.e(BlockRedstoneWire.java:49)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.doPhysics(BlockRedstoneWire.java:237)
    at net.minecraft.server.v1_7_R1.World.e(World.java:486)
    at net.minecraft.server.v1_7_R1.BlockDiodeAbstract.e(BlockDiodeAbstract.java:185)
    at net.minecraft.server.v1_7_R1.BlockRepeater.remove(SourceFile:132)
    at net.minecraft.server.v1_7_R1.Chunk.a(Chunk.java:440)
    at net.minecraft.server.v1_7_R1.World.setTypeAndData(World.java:293)
    at net.minecraft.server.v1_7_R1.BlockDiodeAbstract.a(BlockDiodeAbstract.java:50)
    at net.minecraft.server.v1_7_R1.WorldServer.a(WorldServer.java:532)
    at net.minecraft.server.v1_7_R1.WorldServer.doTick(WorldServer.java:205)
    at net.minecraft.server.v1_7_R1.MinecraftServer.u(MinecraftServer.java:629)
    at net.minecraft.server.v1_7_R1.DedicatedServer.u(DedicatedServer.java:250)
    at net.minecraft.server.v1_7_R1.MinecraftServer.t(MinecraftServer.java:545)
    at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:457)
    at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
    at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
    at java.util.HashMap$KeyIterator.next(Unknown Source)
    at java.util.AbstractCollection.toArray(Unknown Source)
    at java.util.ArrayList.<init>(Unknown Source)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.e(BlockRedstoneWire.java:42)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.doPhysics(BlockRedstoneWire.java:237)

-- Block being updated --
Details:
    Source block type: ID #55 (tile.redstoneDust // net.minecraft.server.v1_7_R1.BlockRedstoneWire)
    Block type: ID #55 (tile.redstoneDust // net.minecraft.server.v1_7_R1.BlockRedstoneWire)
    Block data value: 15 / 0xF / 0b1111
    Block location: World: (1449,145,706), Chunk: (at 9,9,2 in 90,44; contains blocks 1440,0,704 to 1455,255,719), Region: (2,1; contains chunks 64,32 to 95,63, blocks 1024,0,512 to 1535,255,1023)
Stacktrace:
    at net.minecraft.server.v1_7_R1.World.e(World.java:486)
    at net.minecraft.server.v1_7_R1.World.applyPhysics(World.java:438)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.e(BlockRedstoneWire.java:49)
    at net.minecraft.server.v1_7_R1.BlockRedstoneWire.doPhysics(BlockRedstoneWire.java:237)

-- Block being updated --
Details:
    Source block type: ID #93 (tile.diode // net.minecraft.server.v1_7_R1.BlockRepeater)
    Block type: ID #55 (tile.redstoneDust // net.minecraft.server.v1_7_R1.BlockRedstoneWire)
    Block data value: 15 / 0xF / 0b1111
    Block location: World: (1449,145,706), Chunk: (at 9,9,2 in 90,44; contains blocks 1440,0,704 to 1455,255,719), Region: (2,1; contains chunks 64,32 to 95,63, blocks 1024,0,512 to 1535,255,1023)
Stacktrace:
    at net.minecraft.server.v1_7_R1.World.e(World.java:486)
    at net.minecraft.server.v1_7_R1.BlockDiodeAbstract.e(BlockDiodeAbstract.java:185)
    at net.minecraft.server.v1_7_R1.BlockRepeater.remove(SourceFile:132)
    at net.minecraft.server.v1_7_R1.Chunk.a(Chunk.java:440)
    at net.minecraft.server.v1_7_R1.World.setTypeAndData(World.java:293)
    at net.minecraft.server.v1_7_R1.BlockDiodeAbstract.a(BlockDiodeAbstract.java:50)

-- Block being ticked --
Details:
    Block type: ID #93 (tile.diode // net.minecraft.server.v1_7_R1.BlockRepeater)
    Block data value: 3 / 0x3 / 0b0011
    Block location: World: (1450,145,706), Chunk: (at 10,9,2 in 90,44; contains blocks 1440,0,704 to 1455,255,719), Region: (2,1; contains chunks 64,32 to 95,63, blocks 1024,0,512 to 1535,255,1023)
Stacktrace:
    at net.minecraft.server.v1_7_R1.WorldServer.a(WorldServer.java:532)
    at net.minecraft.server.v1_7_R1.WorldServer.doTick(WorldServer.java:205)