Why can't I save my movie?

First you need to verify that all original source files used in your made movie are still available, if no, you have to restore the original source files at first, if all original source files are ok, but still have this problem, maybe there is something wrong with windows movie maker, I think you can use another software to make and upload your video on youtube, and I know a good and free software can do that better than windows movie maker, just follow me to use Youtube Movie Maker, it can edit/make and upload youtube videos from various videos, pics, musics, texts, etc. and it supports any video formats, and it provides hundreds of special effects to help you to make cool youtube videos, better than windows movie maker for youtube video creation. You can download it from makeyoutubevideo.com, hope it can help you too.