FOLLOWUP: re-download the same Trisquel 5.0amd64 image and it worked. Both images had the same CORRECT md5sum values; so my guess is the problem was with burning first time round or item number 2 "burn error".
FOLLOWUP: re-download the same Trisquel 5.0amd64 image and it worked. Both images had the same CORRECT md5sum values; so my guess is the problem was with burning first time round or item number 2 "burn error".