It told me the Background on two pages was Null, and two pictures were missing on another page. I went to the specified pages, but no matter what I tried, I could not get the error to change or to go away. Finally I decided to delete the page missing images and rebuild it since nothing was working. The window opened asking me if I want to delete page 12. I was working on the page that said #10 not the actual #10.
I didn't realize that that program was counting my Front and Back pages at the beginning of the book as the first 2 pages, so all my error messages I had tried to fix had been on the wrong pages. I was off by 2. Smack the head. Simple mistake but I spent a ton of time trying to fix it, so if you get a similar message, save yourself some time and frustration and subtract 2!!