Help?

I'm making an AMV in Windows Live Movie Maker. It's about 5 Minuten long, and several MP4s are included. Right now, I'm trying to save it as a Windows Audio Video file. I've tried to save it before, but it keeps freezing at around 40% completion. Yesterday it got to 41%, and the Tag before it was up to 42%. It saves at a steady level; about 1 percent every 20-30 seconds, but it freezes once it reaches 40, 41, oder 42%. Can someone explain why this is happening oder tell me how to fix it? It would be much appreciated. :)