Export the file to IDML (File>Export and choose IDML)
Open the IDML file - resave it as a new file name (not over the original)
Try it now.
Thank you Eugene for your reply, but what you suggest it doesn't work.
I never had this problem before, just from the latest 2 updates
Ok if that didn't work then there are other options.
You can try the divide and conquer method.
Export half the book to a PDF and if that half makes then it's fine.
Export the other half.
whichever half fails is where the problem is.
Keep halving your export pages in the page range where it's failing until you find the culprit page(s).
Once you narrow it down. You can try removing half the content from that page.
Then the other half.
Again - narrow it down to the problem page.
Whereas an update may have cause the problem - the IDML route could fix it - and where it can't - then you need to find the problem and fix it.
Hope this helps.