My Windows Movie Maker makes my movies to freeze, how can stop this from happening?

I've been working with Windows movie maker version 2011 lately for my school projects and applications for scholarships and universities. The first time, I worked with windows movie maker I was using my friend's computer the version was older than mine and while we were editing the video, the video was freezing. Once we saved the entire project we thought the freezing would stop once we had saved our project, but unfortunately it saved with all the freezing spots. Today, I'm working with another project with my computer and it's doing the same thing. How can I fix this? I've seen this problem all over the internet and no matter what version you have it freezes up. I think it's time for windows to do something about it