SD clone aborts at startup

[2stepbay]

I am not able to startup from my Cloned drive (full backup). My HD has been on the sluggish side of late so I thought I'd zero erase it in case there were bad blocks, then copy my clone back to the HD.

I'm running 10.5.7 on my Intel iMac.

I'm using a Western Digital Studio drive (750 gb) and FW800. It's partitioned with Time Machine and SD, the later set for 298 GB or the same size as my Intel iMac. I have never had a problem booting from the SD clone.

My first step was to create a current backup of the clone. Used backup all files setting. All green at the end.

Next, I booted from my Leopard Installer, opened Disk Utility and erased/zeroed out the HD. New drive is set as a GUID partition. Next, I quit the Installer Disk. A startup Disk panel appeared. I selected the SD Clone, then restart. Computer started to boot. When the Apple gear appeared, screen went black and computer shut down.

I restarted holding the option key. Clone appeared in the Startup Launcher. Same sequence leading to a shut down.

Is there something I'm missing here? How can I get this drive to boot?

Appreciate any guidance. Thanks