Video mode not supported

Why is it that I get this error if i try to set the resolution of my screen to 800x600… 1024x768 works, 640x480 works and even 832x624 works (and some others), but not 800x600. 800x600 worked on windows (when i still had it) and nothing has changed (gfx card, monitor, etc all the same). Is there any way I can fix it? My gfx card is an Nvidia one.

Moved to Hardware