Ok i managed to recreate 8 ligths and when I create number nine all lights go off.
I tried to work in 8bpc 16 bpc and 32 bpc, and I tried to lower all lights to 100 intensity, and disabled the falloff, but nothing helps…
Unfortunately my timezone tells me that I have to go to sleep now.
I have a similar computer at my office and will try to open the project there, first thing tomorrow.
This is due wednesday so hopefully I will solve it before my boss explode…