What motherbd do you have and which port is the optical drive connected to?
Well, I dunno what I did wrong the last time ... but I burned a new Hiren's 15.2 disk and it works fine on my system, including the WD DLG. Thanks for encouraging me to try again.
Just to be complete, my mobo is an Asrock Z77 Extreme 6. The optical drive is on one of my SATA2 ports (but I don't remember which one).