dual monitor setup, DVI connected monitor doesnt have the proper resolution

dual monitor setup, DVI connected monitor doesnt have the proper resolution

I have dual monitor setup with Ubuntu 12.04 but the monitor that is connected via DVI has some resolutions that are not proper (the proper resolution is 1440x900) and in the display settings it is marked as unknown, but it works fine with the VGA connected monitor which works perfectly with 1440x900. the resolution that I am using now for the DVI monitor is 1152x864. Both monitors are ASUS same version.
the xorg.conf file is like this:
# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig:  version 304.88  (buildmeister@swio-display-x86-rhel47-14)  Wed Mar 27 15:36:45 PDT 2013


Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
EndSection


Section "Files"
EndSection


Section "InputDevice"
    # generated from default
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "auto"
    Option         "Device" "/dev/psaux"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection