Thanks for the replies. It appears that my problem is more serious than it appeared and while they seem unrelated, I think it can't be a coincidence that they all happened within a day of each other. Here's what happened in the order it happened...
1 - The G4 begins giving me an error message that it can't go to sleep because some system program is missing (however, the sleep mode is disabled in preferences).
2 - Midi assignments are screwing up as I described in the original post in this thread.
3 - I'm getting no sound out to my mixer board, thus no sound to the monitors. It had been working fine just hours before and I made no changes to any settings.
4 - Here's the scary one... I can't hear anything in the mixing board, but I am getting sound out of the headphone jack on the Digi001, but the playback is happening at about 1/100 speed (and no, it's not half speed, and yes, I know there's a way to do that in Protools but that isn't what's happening).
The last one makes me wonder if I'm not experiencing some kind of hard drive failure and if that couldn't be causing all the other problems somehow. I don't want to put any money into the G4 because I had planned to upgrade to a Mac Pro 8-core and an 003 in 2-3 months. I may have to up my timetable now though.
Ugh. I'm depressed.