After you run DCPromo, you may receive a NetLogon event in the System event log, indicating a failure to dynamically register DNS records.
Before promotion, the Change primary DNS suffix when domain membership changes box on the Control Panel / System / Network Identification tab was not selected.
Use DCPromo to demote the domain controller to a member server. Select the Change primary DNS suffix when domain membership changes box, and run DCPromo to promote this member server to a DC.
If you haven't run DCPromo yet, after the upgrade, use Regedt32 to navigate to:
Set the data value of the SyncDomainWithMembership value name, a REG_DWORD data type, to 1.