Are you using MM2?
Sorry to ask the obvious... but have you saved your project first before saving it as a movie?

Anyway, this site might not be the best place to ask such question, so try:
http://communities2.microsoft.com/co...sxp.moviemaker
http://www.papajohn.org

Note: The latter also suggests a method to apply a "reverse effect" to a video (a member here asked about it a few weeks ago, I don't remember who).

Peace always,
<jdenny>