Just sorted it out, that wasn`t the problem. I had several instanced and grouped lights and after multpling it around ten times, all those light started to give flickers, while other light that aren`t grouped remained the same. I remmember that in Alpha6 grouped light made 3dsmax crash and file got damaged. Seems like a connection.
edit: somehow the problem appears when I have alot of light rendered at once, those light that are problematic, when rendered alone, work correctly. This is really frustrating.