Nikon explains the banding problem with Nikon D200 in a newly released FAQ. Here’s the explanation:

“The digital imaging artifact commonly known as banding can, in specific and unusual conditions, such as extreme exposure and/or exposure compensation settings and high contrast scenes, become visible.

Nikon has discovered that a limited number of early-production D200 cameras may, in specific and uncommon shooting conditions, record images that can present an excessive pattern of fine pitch lines throughout (long banding).

If you experience this, Nikon will, without charge, evaluate your camera to determine if adjustment to the camera’s image output level is required. Adjustment, if required, will optimize the camera’s image output level, thereby reducing visible banding to a minimal level.

Nikon Technical Support personnel can evaluate an affected image file to (1); confirm that your concern is associated to vertical line artifacts and (2), if adjustment to the camera’s image output level will address the condition.“

Website : Nikon FAQ on the Banding Explanation

Website : Reported Nikon D200 Banding Issues