Issue in demoting Windows Server 2008

Hi, I have two Active Directory domain controllers:
- server1 with Windows Server 2008 R2 Standards
- server2 with Windows Server 2016

I already transferred all FSMO roles to server2; command

netdom query fsmo

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confirms that.
My goal is to demote server1 and shutdown that machine. I ran

dcpromo

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to start demote process, but I got error:

Active Directory Domain Services could not transfer the remaining data in directory partition DC=ForestDnsZones,DC=domain,DC=local to Active Directory Domain Controller \\FQDN_of_a_DC.The directory services is missing mandatory configuration information, and is unable to determine the ownership of floating single-master operation roles. 

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I would need some help to fix this!

Thank you