Fix Event ID 2042 by using the Server 2003 support tool repadmin.exe.
The support tools command is:
repadmin /removelingeringobjects <DestDC> <SourceDCGUID> <NC> /Advisory_Mode
DestDC – DC that has the issues
SourceDCGUID – Source DC GUID used to compare with the DestDC
NC – The distinguished name of the directory partition
/Advisory_Mode option should be used first so you can see what changes will actually be made.
You can then demote the domain controller as you normally would. Clean the metadata afterwards to make sure all remaining data is removed.