Mine seems to be working now. I saw the DEBUG line for the first time as it was decrypting, but it made it through that and I was able to make my selections and start makin'.
If for whatever reason I spoke too soon and something odd happens, I'll post again. Thanks for all the hard work!
Thank you! Sorry about that. I didn't see the other posts about the same thing today. It was a my first post, and didn't see it right away to update it. Looks like I already had that registry key, and have 2 dumps from each occurrence. I see in the other thread you say to mail it to support@makemkv....