Be sure that the V-Ray License Server is running. You can check by opening your Task Manager (Ctrl + Shift + Esc) and clicking on the “Services” tab. You should find a service named “VRLService” and it should say “Running” next to it:
If you cannot find the service, you will need to start it manually. The default location is: C:\Program Files\Chaos Group\V-Ray\
In this location you should see a file named “startvrlservice.exe”.
Clicking this will start the license server and will allow V-Ray to communicate with the USB licensing dongle.
If you are still getting errors try uninstalling all versions of V-Ray currently on your system, and then conduct a fresh install of V-Ray. Older versions of V-Ray may need to be uninstalled as opposed to overwritten.