I was having a problem with 1600x1200..adding this to the screen section in xorg.conf made it work.
Option "AddARGBGLXVisuals" "True" Option "ExactModeTimingsDVI" Option "UseEdidDpi" "FALSE" Option "useEDID" "FALSE" Option "ModeValidation" "NoEdidDFPMaxSizeCheck, NoVesaModes"
I was having a problem with 1600x1200..adding this to the screen section in xorg.conf made it work.
Option "AddARGBGLXVisuals" "True" gsDVI" zeCheck, NoVesaModes"
Option "ExactModeTimin
Option "UseEdidDpi" "FALSE"
Option "useEDID" "FALSE"
Option "ModeValidation" "NoEdidDFPMaxSi