My Skyrim, New Vegas and New Vegas Ultimate are all East European editions [they have been bought not via Steam but from a shelf in a shop]. New Vegas' directory is named "fallout new vegas enplczru", however Skyrim's is named plainly "skyrim" without indication that it's a version for East European country [in this particular case for Poland]. [i don't know whether it matters in any way but current installations are both made completely via Steam [i actually used DVDs only once during the very first installation when I was activating/registering those games on Steam] and I install/use/play only English version of both games.] Region conflict sounds like quite reasonable explanation for those problems. But if that would be the case, I wonder why DarnifiedUI can be activated and deactivated in NMM without any problems. Shouldn't NMM be "unresponsive" to all FNV mods without any exceptions? And yes, FOMM worked like a charm for me [with both first New Vegas edition and New Vegas Ultimate and with dozens of mods I used]: no problems with activation, no crashes, no error messages whatsoever.