Typically this is caused by empty background images. Check the page layouts you have used and particularly the backdrop of the page, if it is a plain color or looks like a picture should be dropped there.
If you selected the "Golden Gate Bridge" background, that is a placeholder for a photo. You need to drag a photo to the background of the page.
THey have - and there are always one or more pages with missing photos - typically a page background that requires a photos hidden behind a page layout that has photos on it - any page that has a grey (rahter than a colored) background requires a photo - either place one or change the background to a color and you will be fine
and abe sure to
Before ordering your book preview it using this method - http://support.apple.com/kb/HT1040 - and save the resulting PDF for reference - the delivered book will match it.