Did you try to check the connection by using any TCP scanning tool (as nmap) and test the server port from your workstation in a following way?
nmap -p 16720 serverIP
What's the result? It is most likely caused by a third-party firewall, anti-virus, or Internet security solution, I would recommend you to double check settings for those. Please check all rules applied to the port 16720. As mentioned previously, it must be open both for TCP and UPD.
On the license server computer please try following steps:
Access your Windows Services list by opening a run box (Windows key + R) and then type services.msc and press return.
Please find the Itoo Software License Server service. It should be running and set to automatic. If so, please have a look in Event Viewer for the error. From there you should identify what's blocking the connection.
Hope it help you to identify where the problem is.