I had this happen once. (9600/250 5.0.1 OS 9.0). I occasionally switch the Mac output to Digidesign with no problem, but usually switch it back before I shut down. A while back I left it set that way at shutdown. After restarting, Protools gave me that error, even after I switched the Mac sound back to internal...had to reboot.
Haven't tried to see if I can reproduce it.
Tom
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