They just wrote me back:
Hello,
Thanks for contacting us regarding this matter, and I'm sorry to hear about the trouble you are having. The error you mentioned is being generated due to an issue with the site release we are conducting at the moment, and we anticipate this issue will be resolved when the update completes, which should happen within about 30 minutes.
We apologize for any inconveniences this issue is causing. If there is anything further I can do to assist you, please don't hesitate to ask!
Sincerely,
Auctiva Support