Krusty Burger

Can anyone help please, I have a 2009 A5 with auto lights, but lately when I unlock the car with the remote when it's dark, the lights (front and back) don't come on. It works about one in 10 times in the dark. The car unlocks normally but no lights. If I open the door and lock and unlock it works (if done immediately) which is very unusual. Does anyone know what the problem is? It worked before no problem and I had the drivers lock changed last month as it was broken (not unlocking with the remote on the drivers door). I haven't changed any settings ie coming home, leaving home, it's the same as it was. Thank you, it's driving me mad.