I've inserted several older parts into an assembly. Somehow, these parts are changing the fog density value of all created lights to an illegal value of 1.468 (the legal range is 0 to 1)
Because of this all created lights are already set to this value of 1.468 and cannot be changed. The field is ghosted and SW provides a dialogue which reads: "Please enter a number from 0 to 1"
The only way out is to cancel out of the light property dialoque. This means no fog lighting can be used in the assembly.