Duplicating book in Aperture - copy no photos

I've experienced an intriguing and apparently difficult to reconcile problem in Aperture.

I have many, many times, duplicated books to make amends, change images or add pages. Never ever a problem.

Today I have duplicated one of my books and I end up with a book, correct layout, correct copy but no images/photos of any sort!

I've done the obvious, rebooted Mac, reprocessed thumbnails, rebuilt Aperture database, etc. Still no luck. So tried duplicating an alternative book. No problem this time correct layout, correct copy and all the images/photos. Tried with the orginal book, still no luck.

The book I was duplicating was a duplicate of a previous book, no problems when creating it, and I can duplicate the book I duplicated it from with no issues. I've added some images and I'm wondering if there is some issue to do with the format of these new images. Anyone encountered this problem or has a solution to suggest? Thanks.

Aperture version is 3.2.4 under OSX 10.6.8 (no I'm not about to update this for a number of reasons). MacBook Pro 2.66Gz i7.