Support Request: Java Error on SMP Client

1st Official Post

    I set up a small IC^2 server for me and a few friends, but every so often when somebody places a block everyone on the server crashes with


    It also seems to persist in one area for awhile then move elsewhere; any blocks placed in the area will most likely crash the game. The mods i have running are:


    Client:
    AudioMod
    Buildcraft v1.8.1.1
    IndustrialCraft^2 v1.15
    Minecraft Forge v1.1.1
    ModLoaderModLoaderMP
    Player's ModLoaderMP Client Fix
    Player's SoundSystem Update


    Server:
    Buildcraft v1.8.1.1
    IndustrialCraft^2 v1.15
    Minecraft Forge 1.1.1
    ModloaderMP
    Player's ModLoaderMP Server Fix
    Flan's MP Utils (Crashes occured before installing as well)


    I also used to have Flan's WWII Guns v3, Flan's Vehicles v4, Flan's Planes v16.1, Gary's TurboModelThingy v2.3.4, and PlayerAPI v1, as well as their respective server versions. All of those are, at this point, uninstalled.
    If it matters I also upgraded the world using IndustrialUpgrade (Going from 1.7.3 with IC 8.55_02 to 1.8.1 with IC^2 1.15) and even though it says only SSP worlds are supported, i see no reason why it should cause an error such as this (however I know very little about Java). After discovering the problem I then ran Chunkster (to no avail)
    I also have no idea which mod specifically is causing the problem (or, however unlikely it may be, the vanilla software), but I decided to post here anyway (a quick forum search turned up nothing).
    Running Java JDK 1.7 64bit
    Code tags not cooperating X(


    EDIT: Appears to happen when a machine is in use NOPE