Both Windows Firewall and the anti-virus firewall were enabled. (This is strange in itself: normally, an anti-virus program disables Windows Firewall.) Disabling Windows Firewall, rebooting, and reinstalling the printer software finally got the wireless printer working again.
But behind any good idea, there is a crook looking to make money, and that's exactly what has spurred smartphone scammers to spread a new Android fake anti-virus program.