I have the same issue here. MAC Sierra OS, x-plane 11 though I am not sure that matters since I never get past the initial install, MacBook Pro 2017 only a few months old , I have tried using stuff it expander, re-downloading, rebooting, downloading with safari, downloading with chrome. I can't get past the same initial message. I also put in a support ticket but have had no reply yet. Anyone? Anyone?