Update: This turned out to occur in older version of Rebex components because the server only allows clients that support Renegotiation Indication Extension. Support for RIE has been released as part of Rebex components 2017R1.There is a hotfix available for this - contact firstname.lastname@example.org if you need it. We will add support for this extension in one of the next releases.
Rebex FTP/SSL 2014 R1 and some earlier versions had a bug that caused unreadable alert names to be reported in this particular TlsException message. This has been fixed in Rebex FTP/SSL 2014 R2:
- SSL: Fixed alert names in TlsException messages.
If possible, upgrade to the latest version of Rebex FTP/SSL to get more meaningful error messages. Otherwise, please create a communication log and post it here (or send it to email@example.com) - we might be able to determine what is going on.