....update
i had to wait for a sata enclosure to arrive but when it did i removed the defective HDD - it and all its contents showed up fine when i plugged it into the 10v that works... i copied what i wanted to save and did a full disk format, twice just to be sure.
then i used carbon copy cloner to duplicate the working 10v hdd onto the formatted one... also i added the chimera bootloader as detailed in a youtube video from geekyranesh...
tried booting up the working 10v from this usb hdd but it didnt show up so i was thinking it had failed but to be sure i refitted to its own 10v, booted and got the exact same error message as before, mentioned in my first post... hmmm...
any suggestions?