Why can't I clone a drive using Disk Utility?

[Psurfer]

Ok. Now all is good (I think) . I moved the new drive to the rear carrier, erased it, and then cloned the source drive again, this time w/DU (restore function). So far, so good. Permissions repair ran ok on it, and no more funky cycling sound.

one oddity though: After repairing perms, I then hit Verify Disk in DU. It said "Could not unmount the drive". Should that concern me?