Hello Tom Jedusor,
Thank you for posting in Q&A forum.
To better understand your question, please confirm the information below so that we can help you better.
1.What error message did you received when you edit Default Domain Controllers Policy?
2.How many DCs are there in your domain?
Meanwhile, you can try to troubleshoot the issue as below.
1.You can try to edit Default Domain Controllers Policy on other DC if you have and check if it helps.
2.You can try to edit Default Domain Controllers Policy using other administrator account (sign in DC using built-in Domain Administrator account or member in Domain Admins) to see if you can.
3.You can try to check if the DC works fine by running dcdiag /v to check the health of this DC.
4.If you have more than one DC, you can check AD replication between all DCs by running commands on PDC.
5.Check if SYSVOL replication is OK.
Hope the information above is helpful.
If you have any question or concern, please feel free to let us know.
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