Problem:

Unable to receive flows on listener port since the port is occupied?

Solution:

The flows are not received on listener port because the port is not free. To solve this problem, you can change the listener port of NetFlow Analyzer or free up the port number from the other application which is using it and then restart NetFlow Analyzer.

To change the listener port, refer the below steps:
https://www.manageengine.com/products/netflow/help/how-to-change-webserver-and-listener-port.html#changelistenerport

Problem:

Unable to receive flows on listener port since the port is blocked by Windows firewall?

Solution:

The flows are not received on listener port because it is blocked by Windows firewall. To solve this problem, you can change the listener port of NetFlow Analyzer to some other port. Another option could be to disable Windows firewall for the UDP listener port (Inbound) to allow flow packets.