On trying to remove a old server from the directory (2003 server in a 2003 forest) I received this error

Failed to configure the service NETLOGON as requested “the wait operation timed out.”

DC demote error

The root problem was that this domain controller had a DNS entry to another domain controller that no longer existed.  It was trying to contact it but couldn’t.  Removing that entry and running dcpromo.exe again solved it.