You should call the AC support phone number and leave an urgent message - they monitor for emergencies that prevent the program from working. Maybe they can log on and look - does the program run on the server and work ?
Yep, AC runs perfectly on the server--which made me think it could be a firewall issue. I'm about to dial in to their customer support login here shortly, and I'll post the results once this situation is resolved for those who may come across something similar.
