When trying to update Server 2012 you may see the error below when using WSUS 3.0 SP2.
To fix the above issue there is an update for Windows Server Update
Services 3.0 Service Pack 2 that is available. Download it from below link.
Once downloaded just run the setup file
Check for updates again..
In my experience this fixes the problem every time.
If you'd rather use the Microsoft Fix it then use THIS link. The reference page can be found at http://support.microsoft.com/kb/822798