#386459
All I can tell you about this is that in order to proceed, the installer needs to get a path from the registry, which is written by Rhino's installer. This path is expected to be found here:
  • HKEY_LOCAL_MACHINE\SOFTWARE\McNeel\Rhinoceros\5.0x64\Install\InstallPath
I suppose that failures to find this might include partial failure of the Rhino installer, removal of the value (or one of its parent keys) by a registry cleaner program, and lack of permissions to read from the registry when running the plugin installer.

I'm unsure which Maxwell version you're on, if v5,[…]