Hi Dave,
Many thanks for your prompt reply; I carried out your instructions but still got the same error after the following lines:
Attempting to convert disk 0
Retrieving layout of disk
Validating layout, disk sector size is: 512 bytes
Backing up the system partition
Creating the EFI system partition
After is has failed, the disk is unbootable so I have to clone it from another 'Master' HDD.
Any other suggestions please?
David