Activity Zone - Lack of night function

I have a SoloCam E40. During the daylight period the activity zone I have set works well. At night though, for some reason it does not pick up the milkman delivering milk. He usually delivers the milk between 5-6 a.m. The milkman has two possible routes to approach my house. One would cause him to appear from the bottom of frame and the other from the top of frame. When he leaves after delivering the milk he always leave in the direction to top of frame. If the camera is missing the milkman, what else is it missing?