By fishing around on the Apple Support site, I finally found an article that addressed my problem. It turns out that I needed to delete the SC folder and restart the computer. Wonder why I didn’t think of that? By the way, this isn’t just a Mac thing — the article has instructions for how to do it in Vista.
It worked like a charm, which is good. But somehow the whole process reminds me of what we all had to go through with Microsoft circa 1995.