I have developed material comprising +/- 172 slides, .48 gb total size. I published it without any issues (took a long time!). I returned to the file today, 2 weeks later, to make corrections. Some of the slides show up as blank in normal slide view! When I preview, everything is there - but I cannot see any graphics, photos, text, or even the headline when viewing in Normal Slide View. Is there some way to "refresh" or fix this? Thank you.