I'm getting the same issue, did you ever find a solution?
or more specifically: "'Renci.SshNet.ScpClient' does not contain a definition for 'DownloadFile' and no extension method 'DownloadFile' accepting a first argument of type 'Renci.SshNet.ScpClient' could be found (are you missing a using directive or an assembly reference?)"
or more specifically: "'Renci.SshNet.ScpClient' does not contain a definition for 'DownloadFile' and no extension method 'DownloadFile' accepting a first argument of type 'Renci.SshNet.ScpClient' could be found (are you missing a using directive or an assembly reference?)"