I am getting a similar error, "Negotiation failed. Requested service is not implemented."
It's actually been intermittent, it failed last week. Started working again for a few days, then failed again this morning.
I was on 2018 R1.1. I tried updating to R3 with the same problem. I'm including logs from 1.1 and 3
2018-10-26 10:04:13.255 Opening log file.
2018-10-26 10:04:13.257 INFO FileLogWriter(1)[13] Info: Assembly: Rebex.Common 2018 R1.1 for .NET 4.0-4.7
2018-10-26 10:04:13.272 INFO FileLogWriter(1)[13] Info: Platform: Windows 6.1.7601 32-bit; CLR: 4.0.30319.42000
2018-10-26 10:04:13.272 DEBUG FileLogWriter(1)[13] Info: Culture: en; Windows-1252
2018-10-26 10:04:13.291 INFO Sftp(1)[13] Info: Connecting to SFTP.RENOWN.ORG:22 using Sftp.
2018-10-26 10:04:13.291 INFO Sftp(1)[13] Info: Assembly: Rebex.Sftp 2018 R1.1 for .NET 4.0-4.7
2018-10-26 10:04:13.291 INFO Sftp(1)[13] Info: Platform: Windows 6.1.7601 32-bit; CLR: 4.0.30319.42000
2018-10-26 10:04:13.291 DEBUG Sftp(1)[13] Info: Culture: en; Windows-1252
2018-10-26 10:04:13.307 DEBUG ProxySocket(1)[13] Proxy: Resolving 'SFTP.RENOWN.ORG'.
2018-10-26 10:04:13.311 DEBUG ProxySocket(1)[13] Proxy: Connecting to 204.115.221.12:22 (no proxy).
2018-10-26 10:04:13.401 DEBUG Sftp(1)[13] SSH: Server is 'SSH-2.0-7.7.1.0_openssh Please call support'.
2018-10-26 10:04:13.410 INFO Sftp(1)[13] SSH: Negotiation started.
2018-10-26 10:04:13.606 DEBUG Sftp(1)[13] SSH: Group exchange (legacy form).
2018-10-26 10:04:13.654 ERROR Sftp(1)[12] SSH: Error occured while receiving SSH packet: Rebex.Net.SshException: Requested service is not implemented.
at Rebex.Net.SshSession.edof(Byte[] adq, Int32 adr, Int32 ads)
at Rebex.Net.SshSession.edoe(Byte[] adn, Int32 ado, Int32 adp)
at Rebex.Net.SshSession.edod()
at Rebex.Net.SshSession.muoc.edpb()
2018-10-26 10:04:13.656 ERROR Sftp(1)[13] SSH: Negotiation failed. Requested service is not implemented.
2018-10-26 10:04:13.657 ERROR Sftp(1)[13] Info: Rebex.Net.SshException: Requested service is not implemented. ---> Rebex.Net.SshException: Requested service is not implemented.
at Rebex.Net.SshSession.edof(Byte[] adq, Int32 adr, Int32 ads)
at Rebex.Net.SshSession.edoe(Byte[] adn, Int32 ado, Int32 adp)
at Rebex.Net.SshSession.edod()
at Rebex.Net.SshSession.muoc.edpb()
--- End of inner exception stack trace ---
at Rebex.Net.SshSession.edny()
at Rebex.Net.SshSession.edoa[a,b](bckp`2 adh, Int32 adi, bckq adj, b adk, a adl, a adm)
at Rebex.Net.SshSession.edoh(murh adv)
at murl.pvue(SshSession awy, Byte[] awz, Byte[] axa, Byte[] axb, Byte[] axc, murb& axd, Byte[]& axe, SshPublicKey& axf)
at Rebex.Net.SshSession.edoj(Byte[] adw)
at Rebex.Net.SshSession.Negotiate()
at Rebex.Net.Sftp.yynz.cqmt(cfxh ame, Boolean amf)
at Rebex.Net.Sftp.lshv(String qi, Int32 qj, SshParameters qk, cfxh ql)
2018-10-26 10:42:15.121 Opening log file.
2018-10-26 10:42:15.125 INFO FileLogWriter(1)[15] Info: Assembly: Rebex.Common 2018 R3 for .NET 4.0-4.7
2018-10-26 10:42:15.127 INFO FileLogWriter(1)[15] Info: Platform: Windows 6.1.7601 32-bit; CLR: 4.0.30319.42000
2018-10-26 10:42:15.127 DEBUG FileLogWriter(1)[15] Info: Culture: en; Windows-1252
2018-10-26 10:42:15.144 INFO Sftp(1)[15] Info: Connecting to SFTP.RENOWN.ORG:22 using Sftp.
2018-10-26 10:42:15.144 INFO Sftp(1)[15] Info: Assembly: Rebex.Sftp 2018 R3 for .NET 4.0-4.7
2018-10-26 10:42:15.144 INFO Sftp(1)[15] Info: Platform: Windows 6.1.7601 32-bit; CLR: 4.0.30319.42000
2018-10-26 10:42:15.144 DEBUG Sftp(1)[15] Info: Culture: en; Windows-1252
2018-10-26 10:42:15.155 DEBUG Sftp(1)[15] Proxy: Resolving 'SFTP.RENOWN.ORG'.
2018-10-26 10:42:15.158 DEBUG Sftp(1)[15] Proxy: Connecting to 204.115.221.12:22 (no proxy).
2018-10-26 10:42:15.243 DEBUG Sftp(1)[15] SSH: Server is 'SSH-2.0-7.7.1.0_openssh Please call support'.
2018-10-26 10:42:15.250 INFO Sftp(1)[15] SSH: Negotiation started.
2018-10-26 10:42:15.421 DEBUG Sftp(1)[15] SSH: Group exchange (legacy form).
2018-10-26 10:42:15.464 ERROR Sftp(1)[21] SSH: Error occured while receiving SSH packet: Rebex.Net.SshException: Requested service is not implemented.
at Rebex.Net.SshSession.fmkq(Byte[] agf, Int32 agg, Int32 agh)
at Rebex.Net.SshSession.fmkp(Byte[] agc, Int32 agd, Int32 age)
at Rebex.Net.SshSession.fmko()
at Rebex.Net.SshSession.itzj.fmlm()
2018-10-26 10:42:15.466 ERROR Sftp(1)[15] SSH: Negotiation failed. Requested service is not implemented.
2018-10-26 10:42:15.468 ERROR Sftp(1)[15] Info: Rebex.Net.SshException: Requested service is not implemented. ---> Rebex.Net.SshException: Requested service is not implemented.
at Rebex.Net.SshSession.fmkq(Byte[] agf, Int32 agg, Int32 agh)
at Rebex.Net.SshSession.fmkp(Byte[] agc, Int32 agd, Int32 age)
at Rebex.Net.SshSession.fmko()
at Rebex.Net.SshSession.itzj.fmlm()
--- End of inner exception stack trace ---
at Rebex.Net.SshSession.fmkj()
at Rebex.Net.SshSession.fmkl[b,c](lcyp`2 afw, Int32 afx, lcyq afy, c afz, b aga, b agb)
at Rebex.Net.SshSession.fmks(iuco agk)
at iucs.xoag(SshSession azr, Byte[] azs, Byte[] azt, Byte[] azu, Byte[] azv, iuci& azw, Byte[]& azx, SshPublicKey& azy)
at Rebex.Net.SshSession.fmku(Byte[] agl)
at Rebex.Net.SshSession.Negotiate()
at Rebex.Net.Sftp.srhy.frfl(nnui alr, Boolean als)
at Rebex.Net.Sftp.xhez(String po, Int32 pp, SshParameters pq, nnui pr)