[dnanian]

I don't know what kind of drive it is, giantrobot, but it sounds like it's not supported for boot. (I'm assuming you've been using "Backup - all files" and either "Erase, then copy" or "Smart Update" for your backups.)

So, if you want to restore, what I'd suggest is following the alternate "Disk Utility" method in the User's Guide (basically, boot from your install DVD and run Disk Utility from the Installer menu, then use the Restore tab to restore the backup).