Sorry to say, there could be the hardware problem like significant loss of gain on the red channel for some unknown reason....
I think it's not a hardware problem. The camera functions, apart from the green filter, perfectly.
I think some-one opened the camera and inserted a green filter in front of the sensor. Probably to use the D1x for Black-and-white photography. a l
In camera it's possible to change the fileoutput to Tiff and change the B&W processing in which case you get a large file of 16mb and B&W only. But in camera you see the B&W effect.
Other option is to do the B&W processing in Photoshop and keep the color raw. (NEF)