DCPromo error when removing a child domain

I set up a child domain in our lab at work. The child domain controller was a virtual 2008 server. When I tried to run dcpromo to get rid of it, I got the following error:

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Active Directory Installation Wizard
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The operation failed because:

Active Directory could not transfer the remaining data in directory partition
CN=Schema,CN=Configuration,DC=xxx,DC=NET to domain controller yyy.xxxx.NET.

"The RPC server is unavailable."
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OK
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After pouring through Google and tons of forums, I could not find the answer, but everything seemed to point to it being a DNS problem. It turns out, that was indeed the case. On the parent domain controller, I opened up DNS and navigated to the child domain under forward lookup zones. I tried to ping the FQDN of the child domain controller but could not, however, I was able to ping it by computer name.

When I opened up the properties of the child domain in DNS, the name server listed for the child domain controller had its old IP address listed. So I changed it to the new IP address, and suddenly, all of the RPC errors went away and I was able to demote the child domain controller and remove the child domain!

It took me months to figure this out, and all the trouble was because the IP address of the domain controller changed.