How are you getting the raw NEF files into the computer?
I don't have Nikon gear, but I have heard that the Nikon Transfer software can actually alter the raw file format as the photos are being imported to the system, and can cause problems with Camera Raw.
Download a D2X Camera Raw file from the web and see if you can open it.
In PS click Help/About plugins/camera raw. What version is displayed?
the file was from the CF card directly. That file could be opened and edited a few months ago.
It is 126.96.36.199. When I opened jepg file with Camera Raw, the top of the screen showed Camera Raw 4.6. When I right click on a Raw file in Bridge, there was no "open in Camera Raw.." It is Window 7 that I use, but there was no such problem a few months ago. As I have CS 6 on another computer, I use CS 3 only once in a while.