That's more likely to do with DT than anything else, I have over 100 BD ISO's and they all work mounted in VCD with the latest PDVD 7.3 and 8I had that happen to me 2 weeks ago. I was using PDVD with DT. I can't remember the title, but one of the BD title prompted PDVD to popup a message stating that it needs an update in order to play the BD correctly. As soon as I allow it to update, BAM!, it no longer plays any of my ripped ISO's.
So after doing a bit of research online, I switched over to TMT + VCD and no problem as of yet. Definitely ditching PDVD. What a pain that was.