Having completed NV i thought i would try some mods and play again, To start i downloaded Area 51 from Fileplanet and installed it. games crashs everytime now, sometimes even before first splash screen.
Soon as i unload that mod, back to normal, Have tryed several mods all with the samer result, What am i doing wrong?

Am using FOMM to launch.

I've had the same problem with this mod. And after some careful reading of the nexus page it turns out you also need to install this mod http://www.newvegasnexus.com/downloads/file.php?id=39551 in order for it to work. After I install this mod it seems to stop the game crashing on startup when running the area 51 mod.