... then log out and back in again. If need be, run "dpkg-reconfigure gdm" and select "lightdm" (that was already selected in my case, so I don't know if OKing it actually made any difference). You shouldn't need to reboot, but do so if a simple logout doesn't do the trick.
Hi again. Solution #23 in comment #33 worked for me, so many thanks! For those who want to try it, here are the steps:
gksu gedit /etc/pam.d/lightdm
Under the first line "#%PAM-1.0" paste the following:
session required pam_loginuid.so
session required pam_systemd.so
... then log out and back in again. If need be, run "dpkg-reconfigure gdm" and select "lightdm" (that was already selected in my case, so I don't know if OKing it actually made any difference). You shouldn't need to reboot, but do so if a simple logout doesn't do the trick.