Problem with Aperture slideshow export - Some photos don't display!

I have just completed my latest wedding slideshow. It plays as normal in Aperture, but when exported, certain photos don't show... just a black screen. The timings are unaffected. Aperture 3.6, Yosemite 10.10.1

The affected photos seem to be the ones that I am displaying for longer durations. I'm using Ken Burn's theme and if I turn off the Ken Burn's effect on the affected photo it gets exported ok.

Having spent many hours working on this slideshow I'm "slightly" annoyed! This is obviously a bug introduced in Aperture 3.6 or Quicktime on Yosemite, I just hope it can be fixed ASAP. Unfortunately, I guess Aperture is low on the priority list... I have moved the LR, but still rely on Aperture for slideshows!

HELP!