Okay, try copying the preferences.txt file from your vanilla preferences folder to the TGW preferences folder. That way we'll rule out any incompatibility in settings. I can't think of anything else right now...
Edit: If that doesn't work, try starting the mod through the command "RomeTW.exe -mod:tgw". The bat file uses the command "RomeTW.exe -show_err -nm -mod:tgw", and there may be a freak chance that something weird is happening with the -nm... I'm just guessing... There isn't much else that could account for this.