Hello, i was trying IndustrialCraft², I tryed it with a fesh and new minecraft jar with minecraft forge 3.3.7, I was trying to test Energy-O-mat when i crashed, so i will give you the step for reproduce it (i tryed more than 2 times), try it with a new map please :
1) place a Energy-O-Mat
2) place an item in the top right slot
3) Watch the "Saving Chunk" screen, that the last image you will saw of your map until this bug is fixed.
Please, don't forget that the map will still crash each time you try open it again.
Edit: Here is my ForgeModLoader log:
2012-08-20 18:31:42 [INFO] Forge Mod Loader version 2.2.48.135 for Minecraft 1.2.5 loading
2012-08-20 18:31:42 [FINE] Attempting to load mods contained in the minecraft jar file and associated classes
2012-08-20 18:31:42 [FINE] Found a minecraft related file at C:\Users\x\AppData\Roaming\.minecraft\bin\lwjgl.jar, loading
2012-08-20 18:31:42 [FINE] Found a minecraft related file at C:\Users\x\AppData\Roaming\.minecraft\bin\jinput.jar, loading
2012-08-20 18:31:42 [FINE] Found a minecraft related file at C:\Users\x\AppData\Roaming\.minecraft\bin\lwjgl_util.jar, loading
2012-08-20 18:31:42 [FINE] Found a minecraft related file at C:\Users\x\AppData\Roaming\.minecraft\bin\minecraft.jar, loading
2012-08-20 18:31:42 [FINE] Found a mod class mod_MinecraftForge in file minecraft.jar, attempting to load it
2012-08-20 18:31:42 [FINE] ModLoader BaseMod class mod_MinecraftForge found, loading
2012-08-20 18:31:42 [FINE] ModLoader BaseMod class mod_MinecraftForge loaded
2012-08-20 18:31:42 [FINE] Mod class mod_MinecraftForge loaded successfully
2012-08-20 18:31:42 [FINE] Minecraft jar mods loaded successfully
2012-08-20 18:31:42 [INFO] Loading mods from C:\Users\x\AppData\Roaming\.minecraft\mods
2012-08-20 18:31:42 [FINE] Found a zip or jar file industrialcraft-2-client_1.103.jar, attempting to load it
2012-08-20 18:31:42 [FINE] Found a mod class mod_IC2 in file industrialcraft-2-client_1.103.jar, attempting to load it
2012-08-20 18:31:42 [FINE] ModLoader BaseMod class mod_IC2 found, loading
2012-08-20 18:31:42 [FINE] ModLoader BaseMod class mod_IC2 loaded
2012-08-20 18:31:42 [FINE] Mod class mod_IC2 loaded successfully
2012-08-20 18:31:42 [FINE] File industrialcraft-2-client_1.103.jar loaded successfully
2012-08-20 18:31:42 [INFO] Forge Mod Loader has loaded 2 mods
2012-08-20 18:31:42 [FINE] Beginning mod pre-initialization
2012-08-20 18:31:42 [FINER] Pre-initializing C:\Users\x\AppData\Roaming\.minecraft\bin\minecraft.jar
2012-08-20 18:31:42 [FINE] Reading existing configuration file for mod_MinecraftForge : mod_MinecraftForge.cfg
2012-08-20 18:31:42 [FINEST] Configuration for mod_MinecraftForge.SPAWNER_ALLOW_ON_INVERTED found values default: true, configured: true, interpreted: true
2012-08-20 18:31:42 [FINE] Configuration for mod_MinecraftForge written to mod_MinecraftForge.cfg
2012-08-20 18:31:42 [FINER] Pre-initializing C:\Users\x\AppData\Roaming\.minecraft\mods\industrialcraft-2-client_1.103.jar
2012-08-20 18:31:42 [FINE] Reading existing configuration file for mod_IC2 : mod_IC2.cfg
2012-08-20 18:31:42 [FINE] Configuration for mod_IC2 written to mod_IC2.cfg
2012-08-20 18:31:42 [FINE] Mod pre-initialization complete
2012-08-20 18:31:42 [FINE] Verifying mod dependencies are satisfied
2012-08-20 18:31:42 [FINE] All dependencies are satisfied
2012-08-20 18:31:42 [FINE] Sorting mods into an ordered list
2012-08-20 18:31:42 [FINE] Sorted mod list:
2012-08-20 18:31:42 [FINE] mod_MinecraftForge: minecraft.jar ()
2012-08-20 18:31:42 [FINE] mod_IC2: industrialcraft-2-client_1.103.jar ()
2012-08-20 18:31:42 [FINE] Beginning mod initialization
2012-08-20 18:31:42 [FINER] Initializing mod_MinecraftForge
2012-08-20 18:31:42 [INFO] MinecraftForge v3.3.7.135 Initialized
2012-08-20 18:31:42 [FINER] Initializing mod_IC2
2012-08-20 18:31:43 [FINE] Mod initialization complete
2012-08-20 18:31:43 [FINE] Beginning mod post-initialization
2012-08-20 18:31:43 [FINER] Post-initializing mod_MinecraftForge
2012-08-20 18:31:43 [FINER] Post-initializing mod_IC2
2012-08-20 18:31:43 [FINE] Mod post-initialization complete
2012-08-20 18:31:43 [INFO] Forge Mod Loader load complete, 2 mods loaded