Actually the above worked to get me past the error, then I had to fix the hostname to have it agree with the certificate, but now I'm faced with what seems to be a similar issue in the opposite direction:
2017-03-10 09:47:54.809 Opening log file.
2017-03-10 09:47:54.840 INFO Ftp(1)[16] Info: Connecting to --snip--:990 using Ftp 4.0.4700.0.
2017-03-10 09:47:54.840 INFO Ftp(1)[16] Info: Using proxy none.
2017-03-10 09:47:55.230 DEBUG Ftp(1)[16] Info: Connection succeeded.
2017-03-10 09:47:55.230 DEBUG Ftp(1)[16] Info: Upgrading control connection to TLS/SSL.
2017-03-10 09:47:55.292 INFO Ftp(1)[16] TLS: State StateChange:Negotiating
2017-03-10 09:47:55.292 DEBUG Ftp(1)[16] TLS: HandshakeMessage:ClientHello was sent.
2017-03-10 09:47:55.635 DEBUG Ftp(1)[16] TLS: HandshakeMessage:ServerHello was received.
2017-03-10 09:47:55.651 DEBUG Ftp(1)[16] TLS: HandshakeMessage:Certificate was received.
2017-03-10 09:47:55.651 DEBUG Ftp(1)[16] TLS: HandshakeMessage:ServerHelloDone was received.
2017-03-10 09:47:55.651 DEBUG Ftp(1)[16] TLS: Verifying server certificate --snip--
2017-03-10 09:47:55.713 DEBUG Ftp(1)[16] TLS: Certificate verification result: Accept
2017-03-10 09:47:55.776 DEBUG Ftp(1)[16] TLS: HandshakeMessage:ClientKeyExchange was sent.
2017-03-10 09:47:55.791 DEBUG Ftp(1)[16] TLS: CipherSpec:ChangeCipherSpec was sent.
2017-03-10 09:47:55.807 DEBUG Ftp(1)[16] TLS: HandshakeMessage:Finished was sent.
2017-03-10 09:47:55.963 DEBUG Ftp(1)[16] TLS: CipherSpec:ChangeCipherSpec was received.
2017-03-10 09:47:55.979 DEBUG Ftp(1)[16] TLS: HandshakeMessage:Finished was received.
2017-03-10 09:47:55.979 INFO Ftp(1)[16] TLS: State StateChange:Secured
2017-03-10 09:47:55.979 INFO Ftp(1)[16] TLS: Connection secured using cipher: TLS 1.0, RSA, 128bit AES in CBC mode, SHA1
2017-03-10 09:47:55.979 DEBUG Ftp(1)[16] TLS: Session ID:
0000 |CD-31-00-00-E7-4F-AF-0D 90-34-8F-3F-A5-CA-E3-31| .1...O...4.?...1
0010 |CC-F7-AC-8C-8F-2E-35-0B B2-CB-17-31-8C-C1-5D-C8| ......5....1..].
2017-03-10 09:47:55.979 DEBUG Ftp(1)[16] Info: Control connection upgraded to TLS/SSL.
2017-03-10 09:47:55.994 INFO Ftp(1)[16] Response: 220 Microsoft FTP Service
2017-03-10 09:47:56.025 INFO Ftp(1)[16] Command: USER --snip--
2017-03-10 09:47:56.181 INFO Ftp(1)[16] Response: 331 Password required for --snip--
2017-03-10 09:47:56.181 INFO Ftp(1)[16] Command: PASS ********
2017-03-10 09:47:56.337 INFO Ftp(1)[16] Response: 230 User logged in.
2017-03-10 09:47:56.337 INFO Ftp(1)[16] Command: FEAT
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: 211-Extended features supported:
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: LANG EN*
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: UTF8
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: AUTH TLS;TLS-C;SSL;TLS-P;
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: PBSZ
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: PROT C;P;
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: CCC
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: HOST
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: SIZE
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: MDTM
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: REST STREAM
2017-03-10 09:47:56.493 INFO Ftp(1)[16] Response: 211 END
2017-03-10 09:47:56.509 INFO Ftp(1)[16] Command: OPTS UTF8 ON
2017-03-10 09:47:56.665 INFO Ftp(1)[16] Response: 200 OPTS UTF8 command successful - UTF8 encoding now ON.
2017-03-10 09:47:56.712 DEBUG Ftp(1)[16] Info: Starting data transfer.
2017-03-10 09:47:56.712 INFO Ftp(1)[16] Command: PBSZ 0
2017-03-10 09:47:56.868 INFO Ftp(1)[16] Response: 200 PBSZ command successful.
2017-03-10 09:47:56.868 INFO Ftp(1)[16] Command: PROT P
2017-03-10 09:47:57.024 INFO Ftp(1)[16] Response: 200 PROT command successful.
2017-03-10 09:47:57.024 INFO Ftp(1)[16] Command: TYPE I
2017-03-10 09:47:57.180 INFO Ftp(1)[16] Response: 200 Type set to I.
2017-03-10 09:47:57.180 DEBUG Ftp(1)[16] Info: Accepting data connection.
2017-03-10 09:47:57.211 INFO Ftp(1)[16] Command: PORT 192,168,1,14,208,90
2017-03-10 09:47:57.367 INFO Ftp(1)[16] Response: 501 Server cannot accept argument.
2017-03-10 09:47:57.367 DEBUG Ftp(1)[16] Info: Error while starting data transfer: Rebex.Net.FtpException: Server cannot accept argument (501).
at Rebex.Net.Ftp.1SAJuN(Int32 , Boolean )
at Rebex.Net.Ftp.ykKHPZ(EndPoint )
at Rebex.Net.Ftp.2aYAeNZ(String , Boolean , OTxlj , Int64 , String , String , Int64 , FtpTransferState )
2017-03-10 09:47:57.367 DEBUG Ftp(1)[16] Info: Error while initializing data connection.
2017-03-10 09:47:57.367 ERROR Ftp(1)[16] Info: Rebex.Net.FtpException: Server cannot accept argument (501).
at Rebex.Net.Ftp.1SAJuN(Int32 , Boolean )
at Rebex.Net.Ftp.ykKHPZ(EndPoint )
at Rebex.Net.Ftp.2aYAeNZ(String , Boolean , OTxlj , Int64 , String , String , Int64 , FtpTransferState )
at Rebex.Net.Ftp.2aYAeNZ(String , Boolean , OTxlj , 27NpLhZ , Int64 , FtpTransferState )
at Rebex.Net.Ftp.1Qy0ja(String , String , Stream , Int64 , Int64 , 27NpLhZ )