Comment 4 for bug 90261

Same problem here on Xubuntu 7.04

The program 'xfce4-mixer-plugin' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadAccess (attempt to access private resource denied)'.
  (Details: serial 172 error_code 10 request_code 33 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)
** Message: Lautstärkenregler: screen changed: 0

** Message: No valid plug window.

(xfce4-panel:8331): Gtk-CRITICAL **: gtk_socket_get_id: assertion `GTK_WIDGET_ANCHORED (socket)' failed

** (xfce4-panel:8331): CRITICAL **: Ein Element wurde unerwartet entfernt: "Lautstärkenregler".