To troubleshoot why you are not able to change the permissions on an Active Directory Object, try the following steps:

1. Check which account you are signed in with when trying to modify the permissions and make sure that the account you are using has the necessary permissions on the domain controller to make the changes.
2. Verify that the user still has the proper permissions on the selection of the Active Directory object.
3. Check the Active Directory’s object’s ‘Security Settings.’
4. Ensure that the account you are using to try to make the changes is a Domain Administrator account.
5. Restart the domain controller hosting the Active Directory object.
6. Check if Windows Firewall is blocking the necessary ports or if a 3rd party antivirus is blocking access.