Stand by ... will be doing that this afternoon. Good idea. Thank you ...

You should compare session log file from GUI and .NET to see what makes the difference. Or attach them here, so that we can check.

I'm using WinSCP 5.5.2 Build 4130 trying to SSH into an OpenVMS V6.2 VAX system running Process Software SSH V2.4.A {SSH-2.0-ReflectionForSecureIT_6.1.4.0 build 3197 - Process Software SSH for OpenVMS}. Is it that OpenVMS is supported with other settings? I've been working on this for weeks and I give up.

If I use the GUI, setting timeout to 200 seconds and unchecking Optimize Connection Buffer Size, connection is made but tells me: server's host key not found in cache, gives me the key, and then asks me where to put a key to cache. Whether I say YES or NO, I get in without problems. But with the .NET client code (shown below), it dies after a minute at OPEN(SESSIONOPTIONS) saying the following message (I cut it in size because it's way too long a message). I did take the key shown in the GUI and used it with my .NET code but same issue, hangs at OPEN and then gives me same error message:

{WinSCP.SessionRemoteException: Connection has been unexpectedly closed. Server sent command exit status 1. ---> WinSCP.SessionRemoteException: Error skipping startup message. Your shell is probably incompatible with the application (BASH is recommended)." & vbCrLf & " --- End of inner exception stack trace ---" & vbCrLf & " at WinSCP.SessionLogReader.Read(LogReadFlags flags)"

Here is the code I'm using:

Dim SessionOptions As New SessionOptions ' SCP configuration options
Dim Session As Session = New Session ' Linux connection configuration options
Dim Timer As New TimeSpan(2, 0, 0) ' Session Timeout interval: 2 hr, 0 min, 0 sec

With SessionOptions ' Set up session options
.AddRawSettings("PingType", "2") ' Send execute dummy protocol commands
.AddRawSettings("SendBuf", "0") ' Optimize connect buf size, recommend 262144
.AddRawSettings("SshProt", "3") ' Preferred SSH version: SSH-2 only
.AddRawSettings("Shell", "bash") ' SCP protocol: "bash"
.GiveUpSecurityAndAcceptAnySshHostKey = True' Accept any SSH host key
.HostName = Hostname ' Hostname's IP address is in Buf(2)
.Password = Pwd ' Provide decrypted password
.PortNumber = 22 ' Assign SSH channel 22
.Protocol = WinSCP.Protocol.Scp ' Assign SCP protocol
.UserName = Str ' Provide username
End With ' SessionOptions

With Session ' Execute statements referring to Session object
.DisableVersionCheck = False ' Don't check loaded lib against DLL on disk
.DebugLogPath = Path & "Debug\" & Buf(1) & ".log"' Set session debug path
.ExecutablePath = Path1 & "WinSCP.exe" ' Set path to SCP program
.IniFilePath = Path1 & "WinSCP.ini" ' Set path to INI file
.SessionLogPath = Path & "Session\" & Buf(1) & ".log"' Set session transaction log path
.Timeout = Timer ' Set session timeout to two hours
.Open(SessionOptions) ' Call Linux through SCP
Cmd = "./update.sh" ' Command to execute
If VAX = "1" Then Cmd = "@Search_Queue LOOP"' If this is a VAX, change the command
Str = (.ExecuteCommand(Cmd).Output).Replace(Chr(10), Chr(13) & Chr(10))' Linux/VAX execute, TTY capture
OutFile.WriteLine(Str) ' Dump execution text returned to file
Console.WriteLine(Str) ' Dump execution text returned to screen
End With ' Session

Now here's the acknowledgment from OpenVMS saying I connected:

4-Aug-2014 13:23:12 SSH2 (accepted) from user "account" at [ip_address,11813] (PCname)