The operation failed because:

Active Directory Domain Services could not transfer the remaining data in directory partition

the directory service is missing mandatory configuration information, and is unable to determine the ownership of floating single-master operation roles

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So the issue appears to be some sort of corruption that the AD holds but does not seem to exist in the ADSIEdit records:

When I track down the cn=infrastructure record under default domain naming context I can see that it is correctly set, but when I try to OK out of the dialogue, I receive a Operation failed. Error code: 0x20ae

The Role attribute could not be read

00020AE: SvcErr: DSIS-03152965, problem 5003 (WILL_NOT_PERFORM), data 0

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Read the message where the DCPromo fails to demote:

Active directory domain services could not transfer the remaining data in directory partition

DC=forestdnszones,dc=domain,dc=local to active directory domain controller \\dc2.domain.local



You need to change the record on the infrastructure master by opening: CN=NTDS Settings,CN=DCname,CN=Servers,CN=site,CN=Sites,CN=Configuration,DC=domain,DC=local



And correcting the server name to the infrastructure master name

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