Hi Alistair,
Welcome to the Forum!
The most common reason for the particular error message you are seeing, is that you are attempting to install an update that needs to access System Protected areas which requires the signed-in User running the update/installation to have Administrator privileges.
If your User account is a local account this will trigger that error, so you could choose to sign-in as Administrator instead if you have activated the built-in Administrator, or have created a separate Administrator account for yourself then do the update/install while using this account.
Re the 28092 upgrade I must note that this number does not seem correct. Could you double-check the exact details of the update you are having trouble with and post back that information please.
Regards,
Regedit32