In the 4.0 branch at least xfce-mcs-manager segfaults when xfce-settings.xml is empty. It should probably just exit with an error. See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=254467 I've pasted the trace from that bug below. Also whilst the bug reported is on Hurd I see this on Linux too. It happens in the panel's settings plugin. But I also see it when I run xfce-mcs-manager on its own.
Additional information: This trace is from the running the panel. Starting program: /bin/xfce-mcs-manager Program received signal SIGSEGV, Segmentation fault. (bt full) xfce_read_options () at xfce_settings_plugin.c:228 228 for (node = node->children; node; node = node->next) #0 xfce_read_options () at xfce_settings_plugin.c:228 doc = 0x0 node = 0x8085c28 path = 0x8085c28 "" #1 0x018679d6 in xfce_set_options (sm=0x805e178) at xfce_settings_plugin.c:303 i = 25590462 first = 1 #2 0x01867353 in mcs_plugin_init (mp=0x8084f20) at xfce_settings_plugin.c:79 No locals. #3 0x08049ff5 in load_plugin ( path=0x80615d0 "/usr/lib/xfce4/mcs-plugins/libxfce4settings.so") at xfce-mcs-manager.c:127 init = (void (*)(McsPlugin *)) 0x18672f0 <mcs_plugin_init> plugin = (McsPlugin *) 0x8084f20 module = (GModule *) 0x80859e8 #4 0x0804a15f in plugins_load_dir (dir=0x804cc8f "/usr/lib/xfce4/mcs-plugins") at xfce-mcs-manager.c:169 f = ( const gchar *) 0x80615d0 "/usr/lib/xfce4/mcs-plugins/libxfce4settings.so" plugin = ( gchar *) 0x80615d0 "/usr/lib/xfce4/mcs-plugins/libxfce4settings.so" d = (GDir *) 0x805fce0 #5 0x0804a1d0 in plugin_load_all () at xfce-mcs-manager.c:189 pdir = (gchar *) 0x805e0c0 "/usr/lib/xfce4/mcs-plugins" #6 0x0804a54b in main (argc=1, argv=0x101ae84) at xfce-mcs-manager.c:333 act = {__sigaction_handler = {sa_handler = 0x101ae1c, sa_sigaction = 0x101ae1c}, sa_mask = 22371799, sa_flags = 16887336} status = MCS_MANAGER_NONE daemon_mode = 1 std_mgr = 1 i = 16887296 #0 xfce_read_options () at xfce_settings_plugin.c:228 #1 0x018679d6 in xfce_set_options (sm=0x805e178) at xfce_settings_plugin.c:303 #2 0x01867353 in mcs_plugin_init (mp=0x8084f20) at xfce_settings_plugin.c:79 #3 0x08049ff5 in load_plugin ( path=0x80615d0 "/usr/lib/xfce4/mcs-plugins/libxfce4settings.so") at xfce-mcs-manager.c:127 #4 0x0804a15f in plugins_load_dir (dir=0x804cc8f "/usr/lib/xfce4/mcs-plugins") at xfce-mcs-manager.c:169 #5 0x0804a1d0 in plugin_load_all () at xfce-mcs-manager.c:189 #6 0x0804a54b in main (argc=1, argv=0x101ae84) at xfce-mcs-manager.c:333 The program is running. Exit anyway? (y or n)
Fixed it in the stable branch. HEAD should not be affected by this bug.