2003 Server DC Promo

Hi All

I'm current trying to retire my 2003 SBS Server, it was the only domain controller but I now have a 2016 DC will all roles migrated over to it. Issue is when I run DC promo to demote the 2003 server I get an error as it thinks its the only DC in the domain.

The box indicating that this domain controller is the last controller for the domain domain.local is unchecked. However, no other Active Directory domain controllers for that domain can be contacted.
Do you wish to proceed anyway? If you click Yes, any Active Directory changes that have been made on this domain controller will be lost.

Also when the 2003 server is shut down, it still shows as the logon server for clients and users have issues accessing shares on the file server.Any help would be greatly appreciated.

Thanks