It looks like some transactions this afternoon about 4:19 PM Eastern were having trouble being processed by First Data. These are fixed as of 5:12 PM Eastern. Registrants would have seen an error message stating that the Payment Processor Network is Unavailable and to try again. Most transactions were going thru, but races may want to do an email to their incomplete registrations for today. This impacted all merchants using First Data in a random fashion with some transactions successfully completing and some not.
Here are links to the public issue: