We started getting event ID 13 from a our domain controllers:
Certificate enrollment for Local system failed to enroll for a DomainController certificate with request ID N/A from OLDSERVER.domain.local\oldserver (The RPC server is unavailable. 0x800706ba (WIN32: 1722)).
OLDSERVER was a 2003 domain controller and certificate services server that was removed from the domain at least a couple of years ago. All our current DC's are 2008 R2 and the functional level was raised to that as well.
Where can I begin to change which CA is registered for this auto enrollment?