Thanks for your reply. I tried calling Avid, but I got their answering machine.
So after that, I did what I should have done to begin with: I searched the knowledge base at avid.com. Somehow I stumbled upon the answer to my question: The OS update from OS X 10.4.6 to 10.4.7 is to blame. Apparently, the license dongle’s drivers are not compatible with 10.4.7. They are working on a solution to the problem. I just hope that it arrives before I leave for school on Wednesday. Otherwise, I may be stuck with iMovie until October!