Ive found that you tend to get the black lights when you load one light set over another. They are merely lights that didnt get overwritten. Say you had lights 1-10 in a scene and loaded in a new lightset with lights 1-6. Lights 1-6 would be overwritten and lights 7-10 would be left, but turned off. Hence the black lights. Lights also dont get overwritten if they have a different name from the new ones loaded. There may be other reasons but thats one I`ve witnessed myself. To see if this is the cause you could try loading the new lights into a scene with no lights and see if the black lights still appear.