I have been trying and trying to save a movie project "for computer" or "for email" but while it is saving, it says "missing or unusable files"

It said that I should go to options to enable preparing, which I did.

I tried to double click on the files with the yellow broken exclamation point, even to fix or delete them, but the a yellow broken exclamation point appears on more and more files

The project contains video from my Sony camcorder as well as some cell phone video and photos and is about 23 minutes.  Some files say .MTS at the end of them.  I just need to copy it so that my son's basketball team can see their season highlights at our end of the year party.  any help would be appreciated!