Question about Outlook Express

I recently took a video that was about an hour long recorded through FRAPS and loaded it in to Movie Maker. After working on it, I saved it as a Windows Media Audio/Video File. After a few hours, it finished saving and I went to preview it. About 12 minutes in to the video, the video freezes for the rest of the movie until the point that I cut together two different videos. Throughout the whole thing though, the sound continues unabated. I have created a couple other videos before this one that have worked fine, most have been pretty close to the same length. I would greatly appreciate an answer ASAP.

Thank you very much for the help!