Images Missing from a Project

I'm using RoboHelp 2015.

I have a number (about 2 dozen) of screen images that show in project manager with a red X. When I look in Windows Explorer, the images don't appear at all. Is there some way to retrieve the files or must I re-create them.

In Sept, I create pdfs of this project and the images appeared fine. Now they seem to be gone.

Thanks,

MDawn