Socket Exception (wodFtpDLX / wodFtpDLX.NET)

I have five threads processing 200 download requests each for a total of 1000 files through their own instance of an FtpDlx object.

Each client ALWAYS throws this exception when it has processed exactly 130 files:

System.IO.IOException: Unable to read data from the transport connection: An attempt was made to access a socket in a way forbidden by its access permissions. ---> System.Net.Sockets.SocketException: An attempt was made to access a socket in a way forbidden by its access permissions
   at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
   at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
   --- End of inner exception stack trace ---
   at WeOnlyDo.Net.Sockets.SSLSocket.EndReceive(IAsyncResult ar)
   at WeOnlyDo.Net.Sockets.ProxySocket.EndReceive(IAsyncResult asyncResult)
   at WeOnlyDo.Protocols.FTPplain.ReceiveNotification(IAsyncResult ar)

Initiating call: m_FtpDlx.GetFile(Path.GetTempFileName(), "PATH_ON_SERVER");

I can replicate this behavior every single time with a single client or dozens.

I do receive a StateChange event with the above mentioned exception and a state change to Disconnected.

I do recover gracefully from this; however, I am curious as to the root cause.

(Thoughts?)

FtpDLX client settings (options not mentioned use vendor defaults)

  Port:  21
  Protocol:  2   (FTPS)
  Timeout:  0
  Passive:  true
  Blocking:  false
  TransferMode:  0    (Binary)