I used stored host parameters, so login was the same except for adding encryption. Apparently it's a (Yahoo) server problem, as later attempts with CyberDuck didn't work either. Don't know why it worked the first time, unless CD didn't pick up the TLS flag the first time. Yahoo Small Business has indicated they wouldn't accept non-encrypted connections after September, but they still work, so I guess I'll stick with that for now.
Thanks for the reply.
Thanks for the reply.