I have experimented with your suggestions below…
“make an ftmb backup including the media,
move that file to your D: folder and
open it there,
then change the file locations in options to reflect the new location as well (for future actions)”
It all works satisfactorily.
However, a small improvement. It appears that instead of “move that file to your D: folder and open it there”, it may be easier to make the ftmb backup by specifying that its new location would be D: folder thus saving the Move process?
Many thanks for your help.