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 -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
