Ah, Gremlins! Gotta love/hate them. This has happened a few times (usually saying you have a Seat in your cart that you do not. ie. S12). It’s a ghost and the best way is to just contact the Registrar/web through this form. When you fill it in make sure to include what the issue is and what your order is supposed to be: include, event, t-shirt (number, size and colour) for the quickest processing. You may be issued a paypal invoice after the fact to cover any costs. Once payment is is received your order will be processed and you can access the event.