We are having the same problem:
51 mods loaded
Optifine OptiFine_1.2.5_HD_C6
Minecraft Forge 3.3.8.164
FML v2.2.106.176
Forge Mod Loader version 2.2.106.176 for Minecraft 1.2.5
mod_CodeChickenCore : Initialized (CodeChickenCore-Client 0.5.5.zip)
mod_MinecraftForge : Initialized (modpack.jar)
mod_Somnia : Initialized (modpack.jar)
mod_Mystcraft : Initialized (modpack.jar)
mod_NotEnoughItems : Initialized (modpack.jar)
mod_ReiMinimap : Initialized ([1.2.5]ReiMinimap_v3.2_04.zip)
mod_IC2 : Initialized (industrialcraft-2-client_1.97.jar)
mod_IC2AdvancedMachines : Initialized (AdvancedMachines_4.1_client.zip)
mod_BuildCraftCore : Initialized (buildcraft-client-A-core-3.1.5.zip)
mod_BuildCraftBuilders : Initialized (buildcraft-client-B-builders-3.1.5.zip)
mod_BuildCraftEnergy : Initialized (buildcraft-client-B-energy-3.1.5.zip)
mod_BuildCraftFactory : Initialized (buildcraft-client-B-factory-3.1.5.zip)
mod_BuildCraftTransport : Initialized (buildcraft-client-B-transport-3.1.5.zip)
mod_BuildCraftSilicon : Initialized (buildcraft-client-C-silicon-3.1.5.zip)
mod_AdditionalPipes : Initialized (buildcraft-client-DA-additionalpipes-3.1.0.zip)
mod_ComputerCraft : Initialized (ComputerCraft1.4.zip)
mod_RedPowerMachine : Initialized (RedPowerMachine-2.0pr5b2.zip)
mod_ccSensors : Initialized (ccSensors-client-MC125-B017pr2.zip)
mod_CCTurtle : Initialized (ComputerCraft1.4.zip)
mod_crystalWing : Initialized (Crystal Wing 1.2.5.a.zip)
mod_mocreatures : Initialized (DrZharks MoCreatures Mod v3.7.1.zip)
mod_EE : Initialized (EE2ClientV1.4.6.7.jar)
mod_EnderStorage : Initialized (EnderStorage-Client 1.1.3.zip)
mod_IC2NuclearControl : Initialized (IC2NuclearControl_client_v1.1.10b.zip)
mod_ImmibisCore : Initialized (immibis-core_49.1.1_for_1.2.5-client.jar)
mod_InvTweaks : Initialized (InvTweaks-1.41b-1.2.4.zip)
mod_LogisticsPipes : Initialized (LogisticsPipes-BC3-0.2.5B.zip)
mod_MAtmos_forModLoader : Initialized (MAtmos_packaged.zip)
mod_ModularForceFieldSystem : Initialized (mffs_rev6_for_1.2.5-client.zip)
mod_CompactSolars : Initialized (mod_compactsolars-client-2.3.2.10.zip)
mod_IronChest : Initialized (mod_ironchests-client-3.8.0.40.zip)
mod_RedPowerCore : Initialized (RedPowerCore-2.0pr5b2.zip)
mod_NetherOres : Initialized (NetherOres_Client_1.2.1.zip)
mod_Railcraft : Pre-initialized (Railcraft_Client_5.4.7.zip)
mod_RedPowerControl : Pre-initialized (RedPowerControl-2.0pr5b2.zip)
mod_RedPowerLighting : Pre-initialized (RedPowerLighting-2.0pr5b2.zip)
mod_RedPowerLogic : Pre-initialized (RedPowerLogic-2.0pr5b2.zip)
mod_RedPowerWiring : Pre-initialized (RedPowerWiring-2.0pr5b2.zip)
mod_RedPowerWorld : Pre-initialized (RedPowerWorld-2.0pr5b2.zip)
Steve's Carts : Pre-initialized (Steves Carts 1.5.0.zip)
Thermal Expansion : Pre-initialized (ThermalExpansion-client-BC3-1.0.4.1.zip)
TE: Factory Module : Pre-initialized (ThermalExpansion-client-BC3-1.0.4.1.zip)
mod_Transformers : Pre-initialized (TransformersClient v1.3.zip)
mod_treecapitator : Pre-initialized (Treecapitator 1.2.5.e.zip)
mod_TubeStuff : Pre-initialized (tubestuff_49.1.1_for_1.2.5-client.jar)
Balkon's WeaponMod : Pre-initialized (WeaponMod.zip)
mod_WirelessRedstoneCore : Pre-initialized (WR-CBE Core-Client 1.2.2.3.zip)
mod_WirelessRedstoneAddons : Pre-initialized (WR-CBE Addons-Client 1.2.2.3.zip)
mod_WirelessRedstoneRedPower : Pre-initialized (WR-CBE RedPower-Client 1.2.2.1.zip)
mod_IDResolver : Pre-initialized (modpack.jar)
mod_ThaumCraft : Pre-initialized (ThaumCraft2.1.6d.zip)
Minecraft has crashed!
----------------------
Minecraft has stopped running because it encountered a problem.
--- BEGIN ERROR REPORT 77da974c --------
Generated 11/20/12 9:49 PM
Minecraft: Minecraft 1.2.5
OS: Windows 7 (x86) version 6.1
Java: 1.7.0_09, Oracle Corporation
VM: Java HotSpot Client VM (mixed mode), Oracle Corporation
LWJGL: 2.4.2
OpenGL: GeForce GTX 550 Ti/PCIe/SSE2 version 4.2.0, NVIDIA Corporation
java.lang.RuntimeException: unknown character
This was running a yesterday, but for unknown reasons, it will not any longer.