windows server 2008 - DCPromo was unable to remove DNS delegations from the parent zone

This is the error that I got during domain controller removal on windows server 2008. It says the zone is a period (.)? The domain controller demoted successfully with the dcpromo wizard. I checked the other dcs in the domain and everything looked fine except for DNS. I just had to delete DNS references to the demoted server in DNS.

This is the error that I got during domain controller demotion. Is it safe to ignore?
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Active Directory Domain Services Installation Wizard
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DCPromo was unable to remove DNS delegations from the parent zone: .. This could be because you do not have permissions to do so, or because the zone is hosted by a server that does not run Windows. You should delete DNS delegations in the parent zone for this domain. To do so, contact an administrator who is responsible for the DNS zone: ..
The error was:

The RPC server is unavailable.
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OK   
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Thanks