I have almost exactly the same problem as Steve (post Mar 17,20160) re trying to install the latest version of RUT viewer on a W10 system and the install process requiring still requing 5.6msi which is nowhere on my system. I have gone through the same proceses including RegEdit. If you could also send me a link to download 5.6 installer hopefully that will allow me to install 5.6 again and then upgrade to the latest version. Regards, Mike