This is because xubuntu uses the gnome screensaver. A workaround would be to edit /usr/bin/xflock4 to make it use the gnome screensaver (I have no idea about the command you need though).
** Changed in: xfce4-utils (Ubuntu) Status: New => Triaged -- Xubuntu 7.10: command "xflock4" fails https://bugs.launchpad.net/bugs/183480 You received this bug notification because you are a member of Ubuntu Bugs, which is the bug contact for Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs