Comment 17 for bug 219473

this worked-around/solved it for me:

I log in as "myself" over an ssh -X session, then do "sudo polkit-gnome-authorization". On the screen that opens (via the forwarded X session), I then allow "myself" to admin things _remotely_, rather than at a physical session at the server.
The setting to change is under the branch
org > freedesktop > systemtoolsbackends ~ "MANAGE SYSTEM CONFIGURATION"

click GRANT, add yourself from the dropdown list, and __crucially__ select the "Must Be In Active Session" button. (rather than locally, for example)

It will show up in the list as "granted by root", as you ran the tool with Sudo

Full explanation and _all_ credit goes to the original poster "pvdploeg" here:

http://ubuntuforums.org/showpost.php?p=5338789&postcount=24

( to save your headaches he uses an random example username of "PPP" )

This works on all my headless/LTSP boxes; but good luck with yours

Note: the greyed out box changes subtly, it remains greyed out, but its icon is now in colour; there is no need to click the troublesome box anymore!

Test and report please, there are many similar/duplicate bugs to this, we need a concerted effort to pin it down.

Maybe we were all barking up the wrong tree? After all, all these "greyed out when remote" problems are gnome admin applets or similar?

I'm still puzzled by this, but at least I can work properly now.
Fingers crossed+comments/tests please.
I'll leave it to someone with a less mangled policykit install to follow further, I nearly broke all of mine trying to get this bug sorted out :)

Needs a thorough security gaze too, this is simply a workaround in my eyes, though it may (hopefully) lead us to a real answer.