We have several machines exhibiting the same problem: Occasionally, the screen resolution of the machine will reset to 800x600. After the problem occurs, the only way to correct it is to reboot. If you try to reset the screen resolution in settings, etc., you don't get any errors, but the resolution doesn't change (oddly, if you select any resolution other than the previous one (which is the one that you want), it works).
This usually happens either as a result of the console being locked, or after a remote desktop session, where the machine in question was the host.
All of the machines exhibiting the problem are running Windows Vista, they have various nVidia graphics cards, and they either have a single, large monitor (27"), or dual 21" monitors. They are all various flavors of Dell workstations.
We've tried updating the video drivers to no avail. These same machines also exhibit other video problems. For example:
the screen sometimes goes black when Windows switches to the secure desktop (for UAC checks).
the screen often goes black when attempting to unlock a locked console (sometimes you can't see anything, sometimes it is all black except for password textbox, which is visible).
This has affected probably a dozen high-end workstations. Has anyone else seen this problem?