martin wrote:

Anyway, while WinSCP .NET assembly should indeed report a more meaningful error message

This issue has been added to the tracker:
https://winscp.net/tracker/1741

In what environment are you running the code?

Anyway, while WinSCP .NET assembly should indeed report a more meaningful error message, the ultimate cause is probably that it cannot find WinSCP.exe.

See
https://winscp.net/eng/docs/library_powershell#install
https://winscp.net/eng/docs/library_install#installing

Here's the exception stack

Value cannot be null.
Parameter name: path1 (Occurrences: <1>, TrackingId: <2ca09af9-c780-4017-a1ab-c1d36610384f>)

The following exception occurred:

General Information
----------------------------------------
Additional Info:
TrackingId: 912727d7-c1cd-4e1e-89aa-278bd54078d4
Time (UTC): 04/15/2019 18:51:41
MachineName: d98552119a9f
UTC: 04/15/2019 18:51:41

1) Exception Information
----------------------------------------
Exception Type: System.ArgumentNullException
Message: Value cannot be null. Parameter name: path1
ParamName: path1
Data: System.Collections.ListDictionaryInternal
TargetSite: System.String Combine(System.String, System.String)
HelpLink: NULL
Source: System.Private.CoreLib
HResult: -2147467261

StackTrace Information
----------------------------------------
at System.IO.Path.Combine(String path1, String path2)
at WinSCP.ExeSessionProcess.GetExecutablePath()
at WinSCP.ExeSessionProcess..ctor(Session session, Boolean lLog, String additionalArguments)
at WinSCP.Session.Open(SessionOptions sessionOptions)
at Scs.Lms.ActivityWatcher.Core.FileSystems.FtpConnection.EstablishAsync() in C:\Github\iherb\scs\lms\lms.activity.watcher\src\ActivityWatcher.Core\FileSystems\FtpConnection.cs:line 40
at Scs.Lms.ActivityWatcher.Core.FileSystems.FtpFileSystem.GetFilesAsync(String root, String searchPattern) in C:\Github\iherb\scs\lms\lms.activity.watcher\src\ActivityWatcher.Core\FileSystems\FtpFileSystem.cs:line 59
at Scs.Lms.ActivityWatcher.Processor.ServiceProcessor.ProcessAsync(CancellationToken cancellationToken) in C:\Github\iherb\scs\lms\lms.activity.watcher\src\ActivityWatcher.Processor\ServiceProcessor.cs:line 89
at Scs.Lms.ActivityWatcher.Core.SparkHost.SparkHostService.DoWorkAsync(CancellationToken cancellationToken) in C:\Github\iherb\scs\lms\lms.activity.watcher\src\ActivityWatcher.Core\SparkHost\SparkHostService.cs:line 89

Please attach a full exception callstack and full debug log file showing the problem (using the latest version of WinSCP).

This is my code on c#

try
{
string server = ConfigurationManager.AppSettings["server"];
string user = ConfigurationManager.AppSettings["user"];
string password = ConfigurationManager.AppSettings["password"];
string pathToFolder = ConfigurationManager.AppSettings["pathToFolder"];
SessionOptions options = new SessionOptions();
options.HostName = server;
options.Password = password;
options.Protocol = Protocol.Scp;
options.Timeout = TimeSpan.FromSeconds(20);
options.UserName = user;
options.SshHostKeyFingerprint = ""; //I don't use security code
using (WinSCP.Session session = new WinSCP.Session())
{
// Connect
session.Open(options);

// Upload files
TransferOptions transferOptions = new TransferOptions();
transferOptions.TransferMode = TransferMode.Binary;

TransferOperationResult transferResult;
transferResult = session.PutFiles(@"d:\toupload\*", "/home/user/", false, transferOptions);

// Throw on any error
transferResult.Check();

// Print results
foreach (TransferEventArgs transfer in transferResult.Transfers)
{
Console.WriteLine("Upload of {0} succeeded", transfer.FileName);
}
}
return true;
}
catch (Exception ex)
{
Logs.Error(ex.ToString());
return false;
}

My application works on mono/linux and I don't use security code

Exception throws when I try to open session.