Okay - I'm having the same problem which is well dcumented here:
The Fix by Marc Nivens: "Open ADU&C, right click on the domain controllers OU, properties. Go to the policy tab, highlight the domain controller security policy and click permission. Grant the Enterprise Domain Controllers and Authenticated Users groups "apply group policy" permissions. Then run gpupdate and see if the error returns".
I get as far as: "Open ADU&C"... right click on the domain controllers OU, properties (where?)
I don't see either of my two DC's listed in the list under the "Computers" folder in order ...