www.makemkv.com

I managed to get it working. I installed Version 1.17.7 and everything is okay. It downloads the SDF file. After that i installed Version 1.17.8 and voila Makemkv starts und i can rip a bluray. Seems that in Version 1.17.8 the initial download of the SDF is broken.

I have the same problem with a new setup on Arch Linux since yesterday. I will test on another machine, on which makemkv runs since years.