I openend the app, selected M15 from the list, and switched to FOV display. In the Display Options, under the Other section, I selected USNO A2.0 stars. It came up a dialog that said I'd have to locate the file or catalog or something. I clicked OK.

At that point, a large white rectangle appeared and the beach ball started spinning interminably. I could switch to a different app and back. But when I switched back, the white rectangle was still in the foreground. I could move the rectangle around, but not dismiss it. The beach ball never stopped. I had to force quit.

After force quitting, I launched the app again and it came up with the RECALCULATING" in the main window. The beach ball came up and nothing else happened. I had to force quit again.

I tossed the prefs and things are now back to normal.