Thank you for your suggestion, Peter. Unfortunately I had already tried IDML and the problem was is still occurring in CS 5.5 and 6 (although in 5.5 the pasteboards look different to my screen shot above, one page's board sticks out to the left and another's to the right).
I've deleted the whole chapter that contained the problematic pages, recreated them in a separate document, moved them back into the original document and now it appears to be fine. But I still get an error message on Export!
Do you have any other ideas?
Thanks for your help
Try moving all the pages to a new file. To preserve the relationships, move them before page 1 and then delete what will become the empty last page after the move.
Yup, tried that
I have found a bit of a work around: I PDF'd the first half with no problem, then I tried to PDF the second half - this failed.
Then I PDF'd chapter by chapter until I found that chapter 12 was giving the error message, so I copied and pasted the chapter into a new document and PDF'd that.
The I combined the PDFs into one document in Acrobat.
It's a solution of sorts but still doesn't completely solve the problem of the original working file.
Thanks for the help! Happy holidays!