External Clone not recognized

[chidiar]

Made 2 separate clones. One with CCC and one with Superduper.
When I go to my System Preferences and click StartUp Disk, my MBP does not acknowledge my SuperSuper copy at all even though it is MOUNTED according to my Disc Utility feature.
Now when my CCC clone Drive is mounted, there is absolutely NO problem with StartUp Disk recognizing its presence and it shows in the window.
What could be the issue.
If you can help I would be appreciative.
I have the latest version of SD (for Snow Leopard) but I am using to copy v.10.5.8, SL is not installed yet. Could that be the problem? CCC is for 10.5.8, not upgraded yet to the beta version for SL.
Thank You

[MacCetera]

Look at both drives in Disk Utility - if the SD copied drive's partition scheme is MBR (Windoze Master Boot Record) you will not be able to boot from it, and it won't appear as a selectable drive in the Startup Disk preference panel nor with an Option-boot.
PPC Macs need to be APM (Apple Partition Map).
Intel Macs like GUID best (Group User ID) but will boot from APM as well.
You can select the partition format in Disk Utility under the Options button below the partition map in the Partition panel.

-- Marc

[dnanian]

In addition to what Marc says, if your drive is APM and you're using an Intel Mac, the volume will be hidden in the Startup Disk Preference Pane in OSX 10.5.8 (or so) and later. Use GUID for Intel.