Found this in /var/log/messages:
NetworkManager: <error> [1293967901.401351] [nm-manager.c:1332] user_proxy_init(): could not init user settings proxy: (3) Could not get owner of name 'org.freedesktop.NetworkManagerUserSettings': no such name
The message is repeated 4 times.
Harmless in my case, likely because I'm not using any proxies :)
*** This bug has been marked as a duplicate of bug 655322 ***