Does 1680x1050 Work on X1900/1950 series?

I have an X1900 GT driving a Sony P234B 23" Wide Screen LCD whose native
resolution is 1920x1200.

When I select a 16:10 wide screen resolution of 1680x1050 in display
properties setting, my monitor displays it as if it were 1400x1050 (The
Sony's on-screen info says the resolution is 1400x1050 although my PC says
1680x1050). In other words, the 1680x1050 resolution doesn't fill the full
screen and it seems like 1680x1050 is squashed into 1400x1050, thus making
everything on the LCD vertically elongated. Interestingly, with a resolution
of 1280x800 (another 16:10 WS resolution), I don't have a problem.

The reason why I'm asking is that I want to run games like Call of Duty in
1680x1050, but the above problem prevents me doing so.

I have Cat 6.10 and my PC correctly recognize the monitor as the SONY P234B.
What can be the problem?

 

Problem solved. I used the analog input and 1680x1050 didn't work. Now, I'm
using the DVI and it works beautifully.