Okay, this is just plain weird... I was doing some file rename operations in the Finder, and I get greeted with THIS: The operation could not be completed. (Error -43) Yet, the file renames successfully... but no applications will open the affected file after this happens. The only fix is to restart the Mac - logging out and back in does not help. I have tried verifying the disk (no problems found) and repairing permissions (found and fixed around 15 problems). Neither has helped.