www.makemkv.com

OK, now I deinstalled BitDefender and, o wonder, makemkv works again. I also wrote to the Bitdefender Support Team if the error is known.

OK as if I had known, only the usual stuff. With exceptions and stuff. Won't work for me.
Okay, then I won't use BitDefender anymore.

Same problem. Upgraded to v1.9.9 with Windows 10 and Bitdefender. Fatal Error prevented MakeMKV from running. Solution was to Exclude MakeMKV .exe processes in Bitdefender. Run MakeMKV, input new registration code, then delete exclusions from Bitdefender and MakeMKV works fine.