Failed to convert data connection to TLS

Hello, can anyone please help me with this issue? Thanks.

I use following FTP setting:

     ftp.Port = 21;
     ftp.AuthTls = false;
     ftp.AuthSsl = false;
     ftp.Ssl = false;
     ftp.RequireSslCertVerify = false;

And sometimes I got this error (not always, other times it works):

ChilkatLog:

PutFile:

DllDate: Nov 12 2016
ChilkatVersion: 9.5.0.64
UnlockPrefix: VERISOFTP
Architecture: Little Endian; 32-bit
Language: .NET 4.6
VerboseLogging: 0
RemoteFilename: fileabc.txt.pgp
LocalFilename: C:\\Temp\\TransferFile\\filetest.txt.pgp

ProgressMonitoring:
  enabled: yes
  heartbeatMs: 0
  sendBufferSize: 65536
--ProgressMonitoring
IdleTimeoutMs: 60000
ReceiveTimeoutMs: 60000
ConnectTimeoutSeconds: 10

uploadFromLocalFile:
  localFileSize: 34327
  uploadFromDataSource:
    initialGreeting: 220 FTP Server Ready!
    restartNext: 0
    modeZ: 0
    binaryMode: 1
    pbsz_protp:
      simpleCommand:
        sendCommand:
          sendingCommand: PBSZ 0
        --sendCommand
        readCommandResponse:
          replyLineQP: 200 PBSZ command successful.
        --readCommandResponse
      --simpleCommand
      simpleCommand:
        sendCommand:
          sendingCommand: PROT P
        --sendCommand
        readCommandResponse:
          replyLineQP: 200 PROT command successful.
        --readCommandResponse
      --simpleCommand

    --pbsz_protp
    setupDataConnection:
      passive transfer mode
      setupPassiveDataSocket:
        sendCommand:
          sendingCommand: PASV
        --sendCommand
        readCommandResponse:
          replyLineQP: 227 Entering Passive Mode (170,48,10,109,240,142)
        --readCommandResponse

        dataConnect:
          hostname: 170.48.10.109
          port: 61582
          socketOptions:
            SO_SNDBUF: 262144
            SO_RCVBUF: 4194304
            TCP_NODELAY: 0
            SO_KEEPALIVE: 0
          --socketOptions
          dataConnectSuccess: 1
        --dataConnect
      --setupPassiveDataSocket
    --setupDataConnection
    sendUploadCommand:
      sendCommand:
        sendingCommand: STOR fileabc.txt.pgp
      --sendCommand

    --sendUploadCommand
    Reading intermediate response for upload...
    readCommandResponse:
      replyLineQP: 125 Data connection already open; transfer starting.
    --readCommandResponse

    convertDataConnToSsl:
      ConvertToTls: Elapsed time: 61855 millisec
      Failed to convert data connection to TLS
    --convertDataConnToSsl
  --uploadFromDataSource
  Failed.
--uploadFromLocalFile
TotalTime: Elapsed time: 62416 millisec
Failed.

--PutFile --ChilkatLog