If you are only ordering a Digital Download, click the box next to "BILLING INFORMATION Same as Shipping". If you try to enter a billing address, there is a software glitch that may prevent you from completing your order.
If you are ordering items that need to be shipped, you will not have this problem. Oddly enough, if you live in Canada or Australia, you won't have a problem either way.
If you have questions, don't hesitate to email Lorna (firstname.lastname@example.org).