If you have Windows movie maker, you're probably visiting this blog post because you having problems with being able to save your movie. Windows movie maker has a systemic problem with being able to render movies. Unfortunately, Microsoft doesn't have an answer for you.
If you visit the Microsoft windows movie maker support forums and look up issues where users are not able to save their movies because Windows movie maker becomes nonresponsive; the most the technicians will do in the support forums is ask users to supply activity logs, from which they submit those to an escalation, from which, you never get a response.
It's a ploy to make them look like they're getting your issue the attention and importance that it needs, in the meantime, it's backup 5 yards and punt…