V-Ray for Rhino doesn't render spotlight (but renders the other lights)

I have an enclosed box and whenever I put a spotlight inside it, it never renders. However, all the other tools like linear light render just as they should. Why?
All settings are set to default. I use Rhino 6 with the latest compatible V-Ray for Rhino. Yes, the lights are on in the properties, yes the exposure settings and so forth are fine. When all the lights but default light are off, it renders fine.

Try to set really high values like 10e6 or higher. The default strong but natural decay makes that high intensities are needed.