Custom Share: video part failed to render. Why? What does this even mean?

Have a 38 slide video + soundtrack…lots of work gone into perfecting it. Fails to complete ‘share’ as a Custom Share. Says the video part failed to render!

Fotomagico 5.5.2. iMac OS 10.13.1

Any thoughts

this happened when I changed the pixels in the first screen- (encoded size.
I then changed encoded size to - ‘width’ - and put in ‘1920’.
After that it worked fine