I have encountered the same issue this evening.
---- Minecraft Crash Report ----
// Ooh. Shiny.
Time: 11/10/12 8:56 PM
Description: Exception in server tick loop
java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at ib.b(PlayerManager.java:71)
at ie.b(WorldServer.java:136)
at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:653)
at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:590)
at bcb.q(IntegratedServer.java:110)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:497)
at fp.run(SourceFile:818)
Relevant Details:
- Minecraft Version: 1.4.2
- Operating System: Windows 7 (amd64) version 6.1
- Java Version: 1.7.0_09, Oracle Corporation
- Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
- Memory: 280448960 bytes (267 MB) / 621674496 bytes (592 MB) up to 954466304 bytes (910 MB)
- JVM Flags: 2 total; -Xms256M -Xmx1024M
- AABB Pool Size: 2888 (161728 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
- FML: MCP v7.19 FML v4.2.18.433 Minecraft Forge 6.0.1.355 Optifine OptiFine_1.4.2_HD_B2 38 mods loaded, 38 mods active
mcp [Minecraft Coder Pack] (minecraft.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
FML [Forge Mod Loader] (coremods) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
Forge [Minecraft Forge] (coremods) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
mod_CodeChickenCore [CodeChicken Core] (coremods) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
mod_NotEnoughItems [Not Enough Items] (coremods) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
IC2 [IndustrialCraft 2] (Industrialcraft-2_1.108.71-lf.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
AdvancedMachines [IC2 Advanced Machines Addon] (AdvancedMachines 4.4.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
AdvancedSolarPanel [Advanced Solar Panels] (AdvancedSolarPanels_3_2_0.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
BuildCraft|Core [BuildCraft] (BuildCraft-3.1.8.206.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
BuildCraft|Energy [BC Energy] (BuildCraft-3.1.8.206.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
BuildCraft|Transport [BC Transport] (BuildCraft-3.1.8.206.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
BuildCraft|Builders [BC Builders] (BuildCraft-3.1.8.206.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
BuildCraft|Factory [BC Factory] (BuildCraft-3.1.8.206.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
BuildCraft|Silicon [BC Silicon] (BuildCraft-3.1.8.206.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ComputerCraft [ComputerCraft] (ComputerCraft1.46.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
CCTurtle [ComputerCraft Turtles] (ComputerCraft1.46.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
EnderStorage [EnderStorage] (EnderStorage 1.2.1.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ExtraBees [Extra Bees] (ExtraBees-1.4.1.10-dev-build.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ExtrabiomesXL [ExtrabiomesXL] (ExtrabiomesXL-3.3.0.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
factorization [Factorization] (Factorization-0.6.9_563.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
Forestry [Forestry for Minecraft] (Forestry-1.6.0.0pre6.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ForgeIRC [ForgeIRC] (ForgeIRC-v1.0.11.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
GraviSuite [Gravitation Suite] (GraviSuite_1_4.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
IC2NuclearControl [Nuclear Control] (IC2NuclearControl-1.4.1.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
mod_InvTweaks [Inventory Tweaks] (InvTweaks-1.44-1.4.2.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
IronChest [Iron Chest] (Ironchest-4.2.1.120.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ModularForceFieldSystem [Modular ForceField System V2] (ModularForceFieldSystemV2.2.8.0.5.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
Mystcraft [Mystcraft] (Mystcraft-1.4.1-0.9.3.02.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ObsidiPlates [Obsidian Pressure Plates] (Obsidiplates-1.0.0.1.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
PortalGun [PortalGun] (Portalgun1.4.2v0.2.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
Railcraft [Railcraft] (Railcraft_6.7.0.0.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
mod_ReiMinimap [mod_ReiMinimap] (ReiMinimap_v3.2_05.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
StevesCarts [Steve's Carts] (StevesCarts2.0.0.a20.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ThermalExpansion|Core [Thermal Expansion] (ThermalExpansion-2.0.5.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ThermalExpansion|Factory [Factory] (ThermalExpansion-2.0.5.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
ThermalExpansion|Energy [Energy] (ThermalExpansion-2.0.5.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
TwilightForest [The Twilight Forest] (TwilightForest-1.12.2.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
GregTech_Addon [GregTech-Addon] (GregTechmod.zip) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available->Available
- Is Modded: Definitely; 'forge,fml'
- Profiler Position: N/A (disabled)
- Vec3 Pool Size: 1874 (104944 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
- Player Count: 1 / 8; [ih['TheGnomeo'/159, l='Technomancer', x=2.73, y=68.00, z=-2.27]]
- World Technomancer Entities: 4 total; [EntityTFBighorn['Bighorn Sheep'/3, l='Technomancer', x=54.50, y=58.00, z=207.50], EntityTFBighorn['Bighorn Sheep'/4, l='Technomancer', x=54.50, y=59.00, z=206.50], EntityTFBighorn['Bighorn Sheep'/5, l='Technomancer', x=54.50, y=43.00, z=209.50], EntityTFBighorn['Bighorn Sheep'/6, l='Technomancer', x=53.50, y=60.00, z=205.50]]
- World Technomancer Players: 0 total; []
- World Technomancer Chunk Stats: ServerChunkCache: 31 Drop: 0
- Type: Integrated Server