Working at night is a blessing *and* a curse...there's no one around to bother you when you're trying to get stuff done, but when something does go wrong, you have to wait for the next day to fix it...:-)

I got the install discs from our IT guys today and reinstalled Illustrator. That made the error message disappear, and everything seems to be working well now. (FWIW, I also started ignoring the error message and, aside from the UI fonts appearing to be Arial, Illustrator seemed to work well enough. But it's the principle of the thing...:-) )

So, if you're willing to ignore the error, you can probably get by with it; otherwise, reinstalling apparently is the solution.