hhmmmm well all i can suggest is just try making sure geck is upto date (1.4 i think) and maybe restarting your computer (if you just installed it) and maybe reinstalling the game ya know just general trouble shooting
do you tick both the fallout NV esm and the oldworld blues ESM?
EDIT search geck.ini in your start bar then open GECKCustom.ini in notepad look for "bAllowMultipleMasterLoads=0" and change the 0 to 1