Just copy and paste the certificate from Server and Protocol Information Dialog:
https://winscp.net/eng/docs/ui_fsinfo

THank you, do you have a code example showing hos to use SessionOptions.TlsHostCertificateFingerprint?

martin wrote:

On "Windows 7 Professional" the TLS certificate of the FTP server was verified against Windows trusted root certificate.
On "Windows Web Server 2008 R2", it was not. So either you need to update Windows trusted root certificates or verify the certificate from your code using SessionOptions.TlsHostCertificateFingerprint.

See:
https://winscp.net/eng/docs/tls#certificate
https://winscp.net/eng/docs/library_sessionoptions

On "Windows 7 Professional" the TLS certificate of the FTP server was verified against Windows trusted root certificate.
On "Windows Web Server 2008 R2", it was not. So either you need to update Windows trusted root certificates or verify the certificate from your code using SessionOptions.TlsHostCertificateFingerprint.

See:
https://winscp.net/eng/docs/tls#certificate
https://winscp.net/eng/docs/library_sessionoptions

I am running the same .NET routine on two separate servers. On one of them I connect ok on the other the connection fails.

Both use exactly the same protocol, hostname, username and password.

Can anyone suggest why the failing connection fails.