You might be saving it wrong, jackie. I use Windows Movie Maker, and the only time I have had problems with uploading to youtube is when I was first learning to use it and I was saving it wrong. You have to save it to your computer (there should be a little link that says "Save To Computer" on WMM), then just click next until it starts to save to your computer. After that go to youtube and log in. Then hit the "upload" button and find the file. And it should upload.
Sorry if that didnt make sense! It is really hard to remember step by step how to do it, as it is so atomatic for me. ;]