Thank you Ira L and joemikeb for your suggestions. I have tried both but Photos still quits unexpectedly.
Given that Photos has worked flawlessly for me (with that "intelligent massaging", particularly in editing mode!) up until now with my own photos, I suspect that the culprit is a corrupt photo because my attempt at creating a Photo Book involved pictures taken with 2 cameras wielded by others as well as my own iPhone. As Ira L suggested, determining which one is corrupt is probably going to be too hard. And it may well be an issue (for Photos) related specifically to the Photo Book creation process. If it is, let's hope that Sierra fixes it...
Anyway I'm now awaiting the arrival of the Book I created with iPhoto. From the carrier, it looks like this has been printed somewhere in the States and it's therefore likely to get to me in half the time it would have taken if production had been done in Sydney!!
