Error during Session.PutFiles. Files remaining not uploaded.

Public Sub TransfertSCP(scpAtt As scpAccess, xfertpath As String)
   
   Dim sessOpt As New SessionOptions
   With sessOpt
      .Protocol = Protocol.Scp
      .HostName = scpAtt.HostName
      .UserName = scpAtt.UserName
      .SshHostKeyFingerprint = scpAtt.SshHostKeyFingerprint
      .SshPrivateKeyPath = scpAtt.SshPrivateKeyPath
   End With
   Using Session As Session = New Session
      Try
         Session.ExecutablePath = System.AppDomain.CurrentDomain.BaseDirectory() & "ssh\WinSCPnet.exe"

         ' Connect
         Session.Open(sessOpt)
         ' Upload files
         Dim transferOptions As New TransferOptions
         transferOptions.TransferMode = TransferMode.Ascii

         writeLog(app.path_log, app.filename_log, _
                String.Format("Files in {0} to transfer: {1}", xfertpath, Directory.GetFiles(xfertpath).Count), LogLevel.INF)

         Dim transferResult As TransferOperationResult
         transferResult = Session.PutFiles(xfertpath, scpAtt.RemoteFolder, False, transferOptions)

         writeLog(app.path_log, app.filename_log, _
                   String.Format("Files in {0} transfered: {1}", xfertpath, transferResult.Transfers.Count), LogLevel.INF)

         For Each err As SessionRemoteException In transferResult.Failures
            writeLog(app.path_log, app.filename_log, String.Format("ERROR SCP Transfer failed: {0}", err.Message))
         Next

         ' Print transfert
         For Each transfer As TransferEventArgs In transferResult.Transfers
            Console.WriteLine("Upload of {0} succeeded", transfer.FileName)
            writeLog(app.path_log, app.filename_log, String.Format("SCP Transfer successful: {0}", transfer.FileName))
         Next
      Catch ex As Exception
         writeLog(app.path_log, app.filename_log, String.Format("ERROR SCP Transfet {0}", ex.Message))
      End Try
   End Using
End Sub

transferOptions.PreserveTimestamp = False