D'oh! embarrassingly obvious that Blu-Ray not supported.
yes have loaded BDRebuilder and running the backup. So far so good but looks like it may take all night to run so will let you know how it goes tomorrow.
Of note I am backing up to a NAS which I connect to with a Dune box running Zappiti Dukebox to give me an on demand movie style video player...Nice!
Thanks for the prompt response which has really impressed me. Been on other forums where I get nothing. Loving Myce!