Unity-control-center- buttons for authentication to change settings don't work

[horsemanoffaith]

When I open unity-control-center, go to the date/time settings, and click the "Unlock to change these settings" button, I never get the authentication dialog box. I started UCC in a terminal and get the following error:

(unity-control-center:1474): Gtk-WARNING **: Error acquiring permission: Failed to acquire permission for action-id com.canonical.controlcenter.datetime.configure

I've done some Googling, and find some really old discussions of this error, but everything they give to fix the problem doesn't work. Any ideas?