Happens with systemctl poweroff/reboot.

Steps to reproduce:

1) have more than one user logged in
2) systemctl poweroff
3) polkit will ask you for authentication, wait instead of typing password
Result:
dbus errors, then broadcast message about power-off, although nothing happens (pc will not power-off)

Output:

  $ systemctl poweroff
  ==== AUTHENTICATING FOR org.freedesktop.login1.power-off-multiple-sessions ===
  Authentication is required for powering off the system while other users are 
  logged in.
  Authenticating as: vandrus
  Password: Failed to issue method call: Did not receive a reply. Possible 
  causes include: the remote application did not send a reply, the message bus
  security policy blocked the reply, the reply timeout expired, or the network
  connection was broken.
  Failed to issue method call: Access denied

  Broadcast message from vandrus@hollo on pts/0 (Tue, 2012-12-11 11:23:23 CET):

  The system is going down for power-off NOW!

  polkit-agent-helper-1: pam_authenticate failed: Conversation error

All these messages (except for the final fake broadcast message that does not happen in systemd 208 at least) are expected..

I agree that a nicer message should be displayed though.

Yeah, the polkit conversation and the bus calls will timeout. This is intended that way. CLosing.