This isn’t specific to unity-window-decorator. If you go to ccsm → Effects → Window Decoration and change the command to /usr/bin/gtk-window-decorator, that fails in the same way. ~/.xsession-errors has the line
(gtk-window-decorator:19510): Gtk-WARNING **: cannot open display: :0.0
This isn’t specific to unity-window- decorator. If you go to ccsm → Effects → Window Decoration and change the command to /usr/bin/ gtk-window- decorator, that fails in the same way. ~/.xsession-errors has the line
(gtk-window- decorator: 19510): Gtk-WARNING **: cannot open display: :0.0