[JoBoy]

I boot from a clone on a separate hard drive and open Disk Utility on the clone. I then select Macintosh HD and attempt to repair disk. I get a message: The disk "Macintosh HD" could not be unmounted. It also happens when I try to run iDefrag from the clone to defrag Macintosh HD. Repair Permissions works fine. So does Verify Disk. I'm now running OS X v 10.5.6. This has not happened in the past with other versions of Leopard, although I'm not absolutely sure whether this problem started with 10.5.5 or 10.5.6. It does NOT happen when I repair disk on Sandbox while booted from the same clone. Sandbox and Macintosh HD are partitions on the same disk. Any suggestions?