[dnanian]

Well, you've changed two things, one more serious than the other (Snow Leopard is a far greater change than SuperDuper! 2.6.1). Perhaps there's a problem between it and your NAS?

The error you're getting is coming from the system - we've asked it to create the image, and it fails with that error -- which certainly supports the "problems with Snow Leopard and your NAS" theory.