"I have completely overhauled the check for previous versions of Rhino test in the installer and hopefully made the error messages more meaningful. The new installer should be available later today, please download it and give it a try."
"This is the same message appeared when I tried to install the NXT on a new PC. The problem is not the installation of Rhino 5.0, but the update of Rhino 4.0. install the latest SR. Upgrading the Rhino 4.0 the problem disappeared. I hope it helped"