I just found the according .desktop file in /usr/share/gnome/autostart/gnome-wm.desktop and moved it to /usr/share/applications/gnome-wm.desktop . Now the error message is gone.
I just found the according .desktop file in /usr/share/ gnome/autostart /gnome- wm.desktop and moved it to /usr/share/ applications/ gnome-wm. desktop . Now the error message is gone.