Q: iPhoto quits unexpectedly trying to buy book.

any error message or crash report you can post?

LN

First can you create a PDF file of the book to proof read according to this Apple document:  Preview a print project in Photos, iPhoto, or Aperture to avoid issues - Apple Support.  If you can then check for any missing text, photos or other errors.

Now, boot into Safe Mode, Mac OS X: Starting up in Safe Mode, and try to order from there.

What's complicated?  The PDF preview file is for your protection.  If there's a printing error and you have the file that you created before ordering you'll have no problem getting a refund or new printing. 

You have a problem with your particular setup.  It's not normal so the previous post was a workaround till you're able to find out what's amiss with your setup.  If you have some issue with your system or some 3rd party software that may be blocking the process the Safe Mode is a way around it. 

One thing you can try is boot into the Recovery volume (boot with the Command + R keys held down), select disk Utility and repair both the disk permissions and the disk. Reboot normally and try again.

Another is to run the latest Yosemite update from the App Store. 

To check for 3rd party software that my be affecting your Mac download and run Etrecheck.  Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here (and recommended by Apple Support personnel) in the ASC to help identify the more obvious culprits that can adversely affect a Mac's performance.

My iPhoto book just closes when I try to place an order?

Good work, thanks for the report!