This error normally occurs when the certificate has already been installed onto this server.
If you have already installed this certificate and you are trying to enable the correct services on this server for this certificate this can be done using a command like the below :-
Enable-ExchangeCertificate -Thumbprint [THUMBPRINT] -Services "POP, IMAP, IIS, SMTP"
You will need to replace [THUMBPRINT] with the certificate thumbprint.
If you have installed this certificate correctly onto this server you will need to look through the certificate store and remove the certificate with the thumbprint in the error message. (This is only recommend if you have not tried to installed the certificate on this server before or if the current certificate installed is not working correctly.)
**please also note that the thumbprint and serial number are different fields within the certificate