Cannot select Airplay Device for Output Audio

I can't select my chosen AirPlay device for Output Device. It shows up as one of the options in the Sound System Preference, the Sound Selector in the Menu Bar or the AirPlay selector in iTunes (version 11.0.1). But, when I select it, it automatically re-selects the built-in speakers. Rebooting is the only way to restore this functionality. Even then, it seems to work for a time, then quits working. This problem has been reported elsewhere with no resolution that I'm aware of. Any ideas? 😕