hello Linda i had the same problem like you ...sorry my English a little poor but i hop that i can tell you what i want to say 
when saving the movie look what is written there and choose all files and then save it at the your library at this way i did solve the problem of saving
but i have a problem with sharing ....even i have channel at the you tube but i can't log inn from the movie maker 
and i don't understand why they put that we can share at the face book when we can not after i try to publish my movie on the face book it shows black 
so please if you find the solution for this problem please send to me