I have plenty of space left on my computer. I've been able to modify the file just fine, it's just that if I try to save the file twice in the same session, it doesn't work. I assume that means that I have modify permissions, since I am able to make changes. Something may have happened with MO, I'm not sure. I currently have the esp in the base Steam New Vegas directory, not Mod Organizer's own profile. The game is installed in C:/Program Files, yes. The strangest thing is that this hadn't been happening until a few days ago, so it could be due to some edit I made that somehow corrupted some part of the esp. From what I can tell, editing any other esp works fine, it's just this one.