Can't immunize "All users"

Appologies if this has been asked before, I did search but came up empty.

Usually when taking a look at the immunization list, every user on the machine is listed but there is usually no entry for "All users". This is fine an immunization goes smoothly. However, on a handful of machines I have noticed the entry for "All users" and it can't be immunized. I am typing this on a machine that has this issue. "All users" is listed as any normal user would be, with 4 sections, Cookies, Domains, IPs and Secure Domains, but with 0 items protected.

I believe it shouldn't be in the list at all but so far haven't been able to figure out why it sometimes does. I have ruled out any software from the thread "Various reasons for incomplete immunization".

All I can think of is that maybe somewhere in the registry, the "All Users" account has been altered to show as a regular user, but I may just be thinking out aloud.

Anyone else had this issue and can shed some light onto how I might fix it?

Cheers.

Do you have Administrator credentials?
If running Vista or later, did you "Run as administrator"?

At any rate, usually a local user profile will be used by the browser, not the All Users profile...