Have anybody ever experienced problem w/ D1X when taking a long exposure? My office's D1X develops some kind of snowy-like noise when making a long exposure. This happens for exposure over than 4 seconds. Is it the D1X that unable to handle longer exposure or there was someting wrong w/ the camera? Please help. Thanks.
What ISO gain are you shooting at? That will cause "snowy" noise.
Doesn't the D1X have a noise-reduction mode? Have you tried that? All digital cameras are prone to noise in long exposures. I did some long exposures with my D100. You can see what "dark current" noise looks like here:
I'd guess from your description that you're seeing 'warm' pixels in your images. Take a look at the DPReview D1x night photography examples (near the bottom of the linked page) to see this effect - in particular look at the crop from the image of the ship.
If this is what you're seeing then it isn't a fault with the camera - it's simply down to the fact that it's nigh on impossible for the manufacturers to produce an absolutely perfect CCD. You only worry about problems like this if you get 'hot' pixels that look too bright in normal shots, or 'stuck' pixels that are always visible in any shot.
As Victor has mentioned some newer cameras (such as the D100) have noise reduction modes that can greatly reduce this problem. The D1x doesn't have this capability, but it is possible to perform an equivalent process in Photoshop