WINDOWS MOVIE MAKER HELP?

i am trying to save the video i made on windows movie maker as a video file (.wmv, etc), but IT'S NOT LETTING ME. it goes up to lke 70%, then it says to make sure i have enough free space on my computer or make sure all the original files are there. All the files are there and i have PLENTY of space left. WHAT DO I DO? PLEASE HELP!