I just heard back from Dave Nanian at Shirt Pocket. (On a Sunday during the Super Bowl! I love that company.)
Here is his message:
Time Machine stores its local snapshot in the .MobileBackups folder on the source drive when you're using a laptop.
Rarely, this folder is in a state that makes it uncopyable. If you get an error like this, there are four things you can do:
• Wait for the next actual Time Machine backup to occur, which will flush the folder
• Temporarily turn Time Machine off, which clears the snapshot
• Use "sudo tmutil disablelocal" to turn off local snapshots
• Create and use a copy script that ignores /.MobileBackups (which is more complex for the user, but will be the default in the next version of SuperDuper.
So that's the answer. You can ignore the second two suggestions. When the next version of SD comes out, it will be fixed for good.
BTW, none of this affects SuperDuper users in Snow Leopard or Leopard. It's a Lion-only problem.
Apropos of Lion, I determined that there is no way to downgrade Safari to version 5.0.5. Lion 10.7.0 shipped with, and requires, 5.1 or later. Now we just gotta wait for Apple to fix the mess.