this tends to happen when the picture format is not quite right for some reason; if the control track programming was not done correctly you will get a 'No Data' message when the picture should appear.

Compare carefully the information panel properties of the pics that show with the properties of the ones that don't. Maybe reduce the colours to 256 if the pixel size and standard jpg saving checks out ok?

if you have no luck, I'll mail you, after all we'd want your grandaughters to be in their own slideshow!