I've had this issue as well, but I managed to fix it! What I ended up doing was taking the guide's wording to heart: that is, making sure neither Steam nor Fallout New Vegas was installed in Program Files (x86) on the C drive. Once I moved my Steam install to my second drive, I was able to FINALLY start the game through Mod Organizer, and can now finally continue with installing F&L. Watch the video that is referenced in the guide, it really helps! All in all, I think having F:NV installed separate from the Steam install folder is the root of this problem. Moving Steam from Program Files (x86) is just an added bonus, in my eyes. Though, a part of me wonders if this is a problem that MO could have fixed by itself if it knew this kind of thing caused an error.
