Hi, I was using Rebex SFTP (2017 R4.1) for .NET 4.0-4.7 (FULL VERSION) and Rebex SFTP (2018 R4) for .NET 4.0 -4.7 (Trial Version).
I tried setting up preferred Host Key algorithm as RSA and still getting the same error.
We are getting this error while connecting to one specific SFTP server using Rebex, but we are able to connect to this SFTP server using other clients such as FileZilla, WinSCP.
Here is the Debug level log while connecting to one specific SFTP server.
2019-03-28 09:29:45.678 INFO FileLogWriter(1)[8] Info: Assembly: Rebex.Common 2018 R4 for .NET 4.0-4.7
2019-03-28 09:29:45.690 INFO FileLogWriter(1)[8] Info: Platform: Windows 6.2.9200 32-bit; CLR: 4.0.30319.42000
2019-03-28 09:29:45.691 DEBUG FileLogWriter(1)[8] Info: Culture: en; Windows-1252
2019-03-28 09:29:45.772 INFO Sftp(1)[8] Info: Connecting to sftp1.xxxxxxxxxxx.com:22 using Sftp.
2019-03-28 09:29:45.774 INFO Sftp(1)[8] Info: Assembly: Rebex.Sftp 2018 R4 for .NET 4.0-4.7 (Trial)
2019-03-28 09:29:45.774 INFO Sftp(1)[8] Info: Platform: Windows 6.2.9200 32-bit; CLR: 4.0.30319.42000
2019-03-28 09:29:45.774 DEBUG Sftp(1)[8] Info: Culture: en; Windows-1252
2019-03-28 09:29:45.883 DEBUG Sftp(1)[8] Proxy: Resolving 'sftp1.xxxxxxxxxxx.com'.
2019-03-28 09:29:46.338 DEBUG Sftp(1)[8] Proxy: Connecting to 23.xx.xxx.104:22 (no proxy).
2019-03-28 09:29:46.937 DEBUG Sftp(1)[8] SSH: Server is 'SSH-2.0-RebexSSH_1.0.6051.2'.
2019-03-28 09:29:46.947 INFO Sftp(1)[8] SSH: Negotiation started.
2019-03-28 09:29:47.226 DEBUG Sftp(1)[8] SSH: Group exchange.
2019-03-28 09:29:47.711 DEBUG Sftp(1)[8] SSH: Negotiating key.
2019-03-28 09:29:47.756 DEBUG Sftp(1)[8] SSH: Received 2048-bit Diffie-Hellman prime (minimum allowed size is 1024 bits).
2019-03-28 09:29:48.158 INFO Sftp(1)[10] SSH: Disconnected by the server ('Internal server error').
2019-03-28 09:29:48.232 ERROR Sftp(1)[8] SSH: Negotiation failed. Disconnected by the server ('Internal server error').
2019-03-28 09:29:48.286 ERROR Sftp(1)[8] Info: Rebex.Net.SshException: Disconnected by the server ('Internal server error').
at Rebex.Net.SshSession.tssd[b,c](dixd`2 aga, Int32 agb, dixe agc, c agd, b age, b agf)
at Rebex.Net.SshSession.tssc[b,c](dixd`2 afy, c afz)
at Rebex.Net.SshSession.tssk(jcqm ago)
at jcqq.xkxw(SshSession bac, Byte[] bad, Byte[] bae, Byte[] baf, Byte[] bag, jcqg& bah, Byte[]& bai, SshPublicKey& baj)
at Rebex.Net.SshSession.tssm(Byte[] agp)
at Rebex.Net.SshSession.Negotiate()
at Rebex.Net.Sftp.mtxo.klsf(kuvq alr, Boolean als)
at Rebex.Net.Sftp.nqyl(String po, Int32 pp, SshParameters pq, kuvq pr)