Thanks, green granite, but with humble respect my question is still unanswered.
Why would a cloned disk be different to its donor? They are the same Seagate Barracuda 7200.12 320GB with 16MB cache. The only difference between the two disks are that the cloned one is running marginally newer firmware and the files on it are physically located differently (as proven by running MyDefrag on the donor before it was cloned and on the clone immediately after the first boot using it).
As well as the fact that the two disks require different Access Modes, I am also puzzled by the fact that Auto doesn't work for the clone; to my simple brain the term Auto implies that the BIOS is able to automatically detect whether CHS or LBA is in use on the boot disk and switch accordingly, whereas Large implies that the BIOS is restricted to using LBA (so won't boot if CHS is in use). My initial setting was Auto, so I presumed that the BIOS was free and able to make a choice. It wasn't until I restricted the BIOS to Large though, that it worked; this appears to be counter-intuitive.
Cheers,
Puzzled of Warks