Node Manager not visible in "Untrusted Nodes" tab with error "Unable to contact any server to check if there is a pending trust request" in the node manager log

Node Manager not visible in "Untrusted Nodes" tab with error "Unable to contact any server to check if there is a pending trust request" in the node manager log

When trying to trust a Node Manager in the TIBCO Spotfire Server "Nodes & Services", after starting the Node Manager service, the Node Manager is not visible under "Untrusted Nodes" tab. The Node Manager log file (nm.log) shows the following message:

INFO 2018-01-05T14:46:11,664-0500 [] nodemanager.trust.CertificateMonitor: Unable to contact any server to check if there is a pending trust request
INFO 2018-01-05T14:46:11,664-0500 [] web.servlet.DispatcherServlet: FrameworkServlet 'mvc': initialization completed in 5757 ms

NOTE: This error occurs when the two-way communication is failing between the Node Manager and the Spotfire Server on the backend registration and communication ports.
  Confirm that the ports used by the TIBCO Spotfire Server and Node Manager for backend communication are open and accessible. To do this, verify the backend registration and communication ports listed in server.xml file in Spotfire server and also in nodemanager.properties in <installation directory>\TIBCO\nm\config folder.

1. Check your firewall settings and verify it allows connections on the backend registration and communication ports.
2. Shut down the anti-virus, if you have any, and then check again.
3. Telnet from Node Manager to TIBCO Spotfire Server and from TIBCO Spotfire Server to Node Manager using the backend registration and communication ports. Use this format: "telnet <IP address> <port>"

Note: If the Telnet fails between Node Manager and Spotfire Server using the backend registration and communication ports, try to change the ports to different ones which are available in your machine.
Also, if the firewall is turned ON on your Node Manager and Spotire Server machines, try to create inbound/outbound rules in the firewall settings to enable communication between Spotfire Server and Node Manager.