Our hosting company had some equipment configuration problems today which resulted in payment errors for some clients. Basically, secure Https traffic was not directed to the right servers. This was not the case for everyone, it depended on what particular web server happened to be handling your transaction.
We have been working with them to fix it and payments are processing OK since 11:30 am.
Sorry for the inconvenience.
Dmitry Buterin, Chief Apricot