Well, I have tried yet another time and still no success with the Basic Training guide. It seems to download fine but will not mount and only gives the error message shown above. I suspect that something in the file is either set up wrong or corrupted somehow as all the other available training guides mount fine.
I do wish someone else could/would try and report if it works for them or not.
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
27" iMac Retina 5K