Can't boot from clone drive

[MadCityGeoff]

Hi, everyone. I'm trying to create a bootable clone of my Macintosh HD drive without success. My computer is a recent Mac Pro running Leopard and the external drive I want to use for backup is a recent 1 TB G-Drive. The G-Drive is formatted as GUID and divided into two partitions, one that I'm using for Time Machine and one that I want to use for cloning my internal hard drive.

I ran Superduper with the erase and copy option. When it was done, I checked the external drive and saw all the expected directories. I rebooted and held down the Option key. The G-Drive partition showed up in the list of available boot volumes. I selected it and I got the gray screen with the Apple logo. Then the system locked up and I had to hit the power button.

Can anybody offer any suggestions?

Also, FWIW, after doing the backup and booting onto the Mac HD, I noticed that the G-Drive runs almost continuously for about 15 minutes.

Thanks!