Comment # 18 on bug 1156501 from Michal Koutn�

IIUC, you're missing the a) the socket to session dbus daemon b) the enviroment
variable telling the path to that socket.

The a) is realized by dbus.socket of the user systedm instance. For other user
units b) is done also by dbus.socket. I can't find where is
DBUS_SESSION_BUS_ADDRESS set for user sessions though (I guess somewhere in PAM
or by display manager (ancestor of user session processes)).

Ad a) Is your user systemd instance running? And is dbus.socket active?