We have temporarily made exams unavailable for purchase and scheduling because we currently do not have any additional time slots available for scheduling.
Our exams will only be available until Sept 30th (see support portal article below), and as a result all exam slots are now full.
We are asking our partner examslocal.com to determine if they might be able to accommodate additional time slots.
If we are able to acquire additional time slots, we will once again make the exams purchasable on http://learn.hortonworks.com/ , we recommend that you check this site later for availability.
Thank you again and apologies for the inconvenience,