My video wont save on windows movie maker, need help?

so, one clip im using pauses itself through playback on windows movie maker, and when i go to save the whole thing, it says theres not enough space. i know that this is the culprit, i think the file may be corrupt. i converted it from MP4 to WMV using format factory. for a few other times on other movies ive made using this, ive changed the file to a AVI and this has worked, but not on this case. what can i do?