Macintosh HD won't unmount

[JoBoy]

I use Sandbox and Macintosh HD volumes on my main internal drive. All backups are done by copying Macintosh HD on the main drive to the backups located on two other internal hard drives and an external Firewire hard drive. The Macintosh HD volume will not unmount when I attempt to do maintenance on it while booted from other internal or external drives, but all of the clones of Macintosh HD do unmount. Among all volumes, there is only one named Sandbox and one named Macintosh HD. All others have unique names. There is no Sandbox going by another name. I have no problem with Macintosh HD when I boot from an install disk (OSX or Disk Warrior).

BTW, I apologize again for accidentally putting this thread in the wrong forum. I'd move it if I knew how.