They restarted 3ds Max. Reset the scene. Tried "Morning." Same thing. The dome light stayed stubbornly black.
It was 2 AM. Alex had a villa exterior due in 12 hours. The client wanted "dramatic, cinematic sunset lighting." vray light gen not working
The fix? Change the to a simple path like C:\VRayTemp (no spaces). Or, in newer versions, update to the latest hotfix. They restarted 3ds Max
Panic.