Luckily, this is not my primary Aperture library, but another one that I started a few weeks ago as I thought my first was getting a bit large. I am unable to open Aperture at all, nor can I copy to or from the drive. Because the drive is (I believe) bad, I can't repair the library, plus, as I mentioned, I can't open Aperture anyways. I can pull the drive, but then how do I get Aperture to redirect itself so that it opens my original library, instead of trying to open this new one? UPDATE Pulled the suspicious drive from my Mac Pro. On restarting, Aperture asked which Library I wanted, adding that one was no longer available. So, I'm back on the original library and things look to be running fine. Unfortunately, I hadn't vaulted yet, so the last month is probably gone. Luckily, I think I already exported the few keepers I had during that time.