Vidding Technology

Basically, I have made a video in Windows Movie Maker and it is saved as a project and everything seems fine, yet when I try to Save Movie File it comes up with an error message, telling me it can't do it and that I should check that the location/files in it to see that they are still available.

I have tried three different locations and, as far as I know, the files are perfectly fine.

I really need to have this video in a suitable format very soon!

Can anyone help?