I am having the same problem. it crashes randomly when using the electric jet-pack, descending in hover-mode. and no, I do not want to just not use the jet-pack.
Minecraft has crashed!
----------------------
Minecraft has stopped running because it encountered a problem; Exception in server tick loop
This error has been saved to C:\Users\lane\Downloads\FTBBETAA\minecraft\crash-reports\crash-2012-11-19_22.17.53-server.txt for your convenience. Please include a copy of this file if you report this crash to anyone.
--- BEGIN ERROR REPORT b393c81a --------
Generated 11/19/12 10:18 PM
- Minecraft Version: 1.4.2
- Operating System: Windows 7 (x86) version 6.1
- Java Version: 1.7.0_07, Oracle Corporation
- Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
- Memory: 44482200 bytes (42 MB) / 352616448 bytes (336 MB) up to 1037959168 bytes (989 MB)
- JVM Flags: 2 total; -Xms256M -Xmx1024M
- AABB Pool Size: 2383 (133448 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 Feed The Beast Mod Pack 37 mods loaded, 37 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
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] (portalgun1.4.2v0.3_universal.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: 481 (26936 bytes; 0 MB) allocated, 392 (21952 bytes; 0 MB) used
- Player Count: 1 / 8; [ih['Lman94'/192, l='ftb1', x=-96.90, y=74.46, z=-3.08]]
- World ftb1 Entities: 0 total; []
- World ftb1 Players: 0 total; []
- World ftb1 Chunk Stats: ServerChunkCache: 0 Drop: 0
- Type: Integrated Server
java.util.ConcurrentModificationException
at java.util.LinkedList$ListItr.checkForComodification(Unknown Source)
at java.util.LinkedList$ListItr.next(Unknown Source)
at ic2.common.AudioManagerClient.onTick(AudioManagerClient.java:105)
at ic2.common.IC2.tickStart(IC2.java:1374)
at cpw.mods.fml.common.SingleIntervalHandler.tickStart(SingleIntervalHandler.java:16)
at cpw.mods.fml.common.FMLCommonHandler.tickStart(FMLCommonHandler.java:116)
at cpw.mods.fml.common.FMLCommonHandler.onPreWorldTick(FMLCommonHandler.java:292)
at net.minecraft.server.MinecraftServer.r(MinecraftServer.java:652)
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)
--- END ERROR REPORT f1050cfb ----------