After a signature update from Avast this morning.....
A critical file for Novabackup: nsMail.dll
was flagged as Trojan and deleted (rather than moved to Virus Chest AS I HAD IT SET TO DO). No options, file simply gone and Novabackup now hosed.
Just a heads-up for anyone else that gets hit with this, that file is 1) NOT infected NOR a Trojan, it's part of Novabackup's installed program, and 2) you have to uninstall Novabackup and reinstall it. The only bright spot in #2 is that when you uninstall it, you can choose to preserve your settings and media catalogs.
Brilliant job there, engineers.