The following error appears when I launch the game : "Error while loading entity prototype "lavaL" (lamp): energy usage per tick can't be negative.
Modifications: the Underground"

If I remove The Underground mod, the error disappears and I can launch the game.

Yea one of the smaller patches released a bug fix for negative energy. So now i got to do some other trickery to light those lava fields =/

Temporary fix released

Can't launch, as it's trying to do something else with the lights that's an issue. "Error in assignID, entity with name 'lavaL' does not exist." It's in the Control.lua, so far as i have found.