alrighty so for your issue first try a few things. Firstly, make try running it as admin and not running it as admin, then try running in in compatibility mode under this tab of properties: http://puu.sh/l3Klp/c76b0f0db9.png
Also, since fomm is rather unstable at certain points it can be tricky to pinpoint exactly what the problem is. But also try moving the folder GeMM from your pgoram files INTO your fallout new vegas / fallout 3 directory and see if that fixes it.
If all that doesnt work, watch this video on how to fix it: https://www.youtube.com/watch?v=Kw-xj7IAlak