I have a ViewSonic VX2235 which has a native resolution of 1680x1050, and a GeForce 9500 GT. I use DVI with this monitor. I use Arch Linux. It has worked fine for a long time until last week when I updated the system (which included xorg 1.8.1). Now this screen will not go above 640x480. I also have a ViewSonic VA720 connected via a DVI to VGA adapter. It has ha native resolution of 1280x1024. It has not been affected by this issue.
This problem appears similar to the one in: http://www.nvnews.net/vbulletin/showthread.php?t=152325
where the poster has a problem with a 23" dell screen attached to his laptop and http://www.nvnews.net/vbulletin/showthread.php?t=152221
where the problem is an LG tv. Also I found this about a Zalman ZM-M220W which has the same navtive resolution as mine, http://www.nvnews.net/vbulletin/showthread.php?t=152042
The last posts suggests I try altering my modeline, which I will try after trying to upgrade to the latest 256.35 version. I have tried various modifications to the xorg.conf file, including disabling TwinView (and enabling) and providing a mode in the "display" section of the "screen" section, without success. Regardless this is definatlly a regresion and I hope it will be fixed in the latest version.
I have attached two nvidia bug reports the new one should be the results with twinview disabled and the old the one with it enabled. I hope any other people have this issue can find usefull information in this post or add any further solutions they may have.