Dear Maintainer,
I can't start Xfce Display Settings after setting dual monitor configuration by
Nvidia X Server Settings. Message is "Unable to start the Xfce Display
Settings".

xorg.conf:
"
# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 304.88  (pbuilder@cake)  Wed Apr  3 08:58:25 UTC
2013


Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 1680 0
    Screen      1  "Screen1" LeftOf "Screen0"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
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

Section "InputDevice"

    # generated from default
    Identifier     "Keyboard0"
    Driver         "kbd"
EndSection

Section "Monitor"

    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "Acer AL1751"
    HorizSync       30.0 - 83.0
    VertRefresh     55.0 - 75.0
    Option         "DPMS"
EndSection

Section "Monitor"

    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "Acer AL2016W"
    HorizSync       31.0 - 84.0
    VertRefresh     56.0 - 77.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GT 640"
    BusID          "PCI:2:0:0"
    Screen          0
EndSection

Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GT 640"
    BusID          "PCI:2:0:0"
    Screen          1
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "metamodes" "DFP-0: 1280x1024_75 +0+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen1"
    Device         "Device1"
    Monitor        "Monitor1"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "metamodes" "DFP-2: 1680x1050_60 +0+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

"

I'm sorry, but I just can't do anything here, please try with the
nouveau driver or something free.

Regards,

I see have the same problem on my system running Debian testing. Iuse
the non-free Nvidia driver with a dual-monitor setup. Starting
xfce4-display-settings just gives a dialog box saying "Kann die
Xfce-Anzeigeeinstellungen nicht starten" in my default locale (or
"Unable to start the Xfce Display Settings" in C locale). The dialog box
has just a "Close" button. There is no further information in the dialog
box, and nothing is written to the terminal from which I started
xfce4-display-settings.

xfce4-display-settings should definitely at least give a more verbose
error message.

Philipp

P.S.: This bug report at Red Hat Bugzilla looks related (at card, but
same error message and multiple monitors):
https://bugzilla.redhat.com/show_bug.cgi?id=1013150