It is possible to have a system with 2 or more NICs serving different subnets. If the VNC Server license key is added when both NICs are enabled, then connections can be made to both interfaces.
License keys are bound to the first network interface found that is available when they are added to the store. VNC Server will check the stored key against the MAC address of the first interface found. If the first network interface is disabled but another one is used, license keys will need to be re-added to the store.
Therefore, if, for example, the cable is removed from the interface to which the license key was bound,
vnclicense -check shows 0/0 desktops free and remote connection attempts fail. The logfile shows:
vncserver license key is invalid, missing or has expired
To work around this, create a script that removes and re-adds keys whenever network interfaces are toggled.
Alternatively, add the license with a dummy MAC address:
vnclicense -SystemId=ffffffffffff -add KEY (where KEY is your 25-digit license key)