Windows Movie Maker says my file is corrupted, but it works fine?

I was trying to make a youtube video of something I did earlier that was sent to me from my mom's iPhone. It was originally a .MOV file but I renamed it as a .AVI file, because Windows Movie Maker doesnt support .MOV. It then said I could not import my file because "the file is not valid or is corrupted." I can open it and it works fine, though. What do I do? How can I import it?