As they've stated, its not an error. Different kind of lights oscillates at different frequencies (they tun on and of a certain amount of times in a second), fluorescent tubes and such, with magnetic ballasts, oscillates at the frequency of your power grid (220v = 50hz // 110v = 60hz). For it not to show on your camera, it must have a shutter speed equal to the Hz of it, or, it must be a number equal to the base Hz multiplied by a natural number (1, 2, 3, etc). It happens on TV screens also.
The thing is that nowdays, many light fixtures uses an electronic ballast, which, in theory, oscillates at such a high frequency that the camera shouldn't be able to pick it up. But not every manufacturer uses good ballasts. So sometimes it is really hard to find the right shutter speed. It has happened to me with many stage lights, I flicked the shutter dial everywhere in live view until I got the effect toned down the most, but I couldn't remove it all the way. This applies a lot when it comes to LED lights. They are a bitch.