You seem to be using "Rebex SFTP" (file transfer over SSH) instead of "Rebex FTP/SSL" (FTPS, FTP over SSL) - please check out our Secure FTP disambiguation page for more information about these protocols and component.
I think you should use Rebex FTP/SSL instead. To skip certificate validation in Rebex FTP/SSL, you can use the following code:
' disable certificate validation - accept any certificate
Dim p As New Rebex.Net.TlsParameters()
p.CertificateVerifier = CertificateVerifier.AcceptAll
Dim f As New Rebex.Net.Ftp()
' not sure whether you need explicit or implicit TLS/SSL
f.Connect(Host, 21, p, FtpSecurity.Explicit)
' f.Connect(Host, 990, p, FtpSecurity.Implicit)
f.Login(UserID, PW)
f.GetFiles("/ftprca/Outbound/epic", "c:\aatemp\", Rebex.Net.SftpBatchTransferOptions.Default, Rebex.Net.SftpActionOnExistingFiles.OverwriteAll)
f.Disconnect()
But please be aware that skipping certificate validation in production environment is greatly discouraged - please check out certificate validation HOWTO for an overview of recommended solutions.