Disappearing photos on JPG export using Corel X6

I am trying to design a photo collage and export it as a JPG.  I have done several before, but this one is removing pictures when I export.  I have tried it as RGB and CMYK as different sizes, qualities etc, but they still do not want to export.  On their own they will, but not with the others.  What on earth is going on?  If anyone can shed some light I would be grateful.  Thank you.