Windows Movie Maker
Just a quick word on it. I am sticking with the program, for those wondering. I just looked into why it's doing what it does, and found it might be the codecs. I turned off the problem codec and thus succeeded in the program not even considering saving movies and coming up with "files missing". I have since turned said codec back on and the movies are saving.
Patience is going to have to be a virtue, by the looks of it.