The issue is with a brand new 890FXA-GD65 motherboard, but likely affects other recent MSI models. When you place a good bootable CD in a working CD drive and attempt to boot it, it tries to load the CD then fails saying its not a valid boot disk.
Trying different cd/dvd drives that are known good and bootable in other machines doesn't fix the problem. Trying other disks about 10 in my case, all of which are good bootable disks on other machines, does not resolve the problem- only 1 in 10 disks would work.
Note: I just figured out the solution to this problem prior to posting this, but I'm going to post it anyway to save the next person with this problem the agony. I didn't see this answer on other questions and it appears to be motherboard specific.