Licensing Server Connection Issue

System.ServiceModel.ServerTooBusyException

Or

This is usually because of a firewall rule on the network. We've seen this in sites where they have strong firewall rules.
The network sys admin will have to allow access to the license server from the problematic terminal.

An easy test is to see if the browser on the problematic terminal can open the following link
https://services.idealpos.com.au/LicensingService/Licensing.svc