Comment 13 for bug 819328

Can someone describe what "You need a policykit agent in your custom x session" means - how does one achieve this? I'm not having much luck finding documentation/guides on this.
'apt-get upgrade' from a console window works for me but update-manager still fails.

Or better yet, is there a guide for "missing" components that one should add in a bare xsession in order to get essential features working like update-manager.