Hi,
When installing our plug-in(s), please double check you are not running any 3ds max or related (like the VRay Spawner) service during the installation process. Sometimes, even closed, 3ds max might not shut down correctly and its processes are still running in the background. To check this you can go to the Task Manager by pressing Ctrl+Shift+Esc and make sure they've both has shut down correctly.
Best regards,