SCSQL backup fails with "Unable to connect to the remote server"

• The SCSQL Plug-in Host is shown with the "Down" status in the SnapCenter GUI Host pane.
• SnapCenter Plug-in for SQL backup fails with the following error message:

  Example:

 2020-04-06T14:01:10.0843263+08:00 DEBUG SnapManagerWeb_269 PID=[9760] TID=[157] Request Data: ****************************
 2020-04-06T14:01:11.1155984+08:00 ERROR SnapManagerWeb_269 PID=[9760] TID=[157] Exception in method: InvokeXML.
System.Net.WebException: Can not connection reomte server ---> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it <IP_of_host>:8145
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
      --- End of inner exception stack trace ---
   at System.Net.WebClient.UploadDataInternal(Uri address, String method, Byte[] data, WebRequest& request)
   at System.Net.WebClient.UploadString(Uri address, String method, String data)
 2020-04-06T14:01:11.1155984+08:00 DEBUG SnapManagerWeb_269 PID=[9760] TID=[157] Plug-in discovery failed. Error: No connection could be made because the target machine actively refused it <IP_of_host>:8145 SnapCenter is able to ping and telnet to the port 8145 of the host