Hi seminarymaltaseminarymalta,
It's not license issue. It's a limitation of Virtual Machine. You can not assign more than 10 network interface (NIC) to a virtual machine. It means you can assign max 9 NIC for downlink and 1 for uplink to your Untangle firewall. If you have 10 southbound VLANs you need to create two firewall VMs.
Thanks!!