One user reported the same problem and found this Apple document solved his problem: Mac OS X: Resetting the SyncServices folder. Give it a try and let us know if it's successful.
If that fails a known workaround is to boot into Safe Mode, Mac OS X: Starting up in Safe Mode, and order the book from there. Be sure to make a PDF copy of the book as described in this Apple document, iPhoto, Aperture: Previewing an order in iPhoto or Aperture, and proof the book before ordering. Keep the pdf file to compare with the printed copy when you receive it.