This is a very rare error, but can happen if you ordered a book on one dotphoto account, then created another dotphoto account with a new sign-in and the same email address, and tried to order from the new account. This confuses the ordering system.
The solution is to alter the signin of the old account -- even changing it, for instance, from barrygibb to barrygibbOLD- - and then to change the signin of the new account to the old account signin -- for instance, barrygibb. When placing your book order, use your current account's new (old) signin -- in this example, barrygibb -- and your order should go through.
Sign in with your email address instead of your dotphoto user name.
When dotphoto asks for a User Name, use your unique email address instead.