After the release of the official version of macOS 10.13 (High Sierra), we tested nessViewer and nessMediaCenter again and could not find any problems.
However, High Sierra showed a different MAC address in the system settings “Network” as well as in nessViewer after the first start – and thus in nessViewer appeared the start dialog with the info “Unregistered full version” also with previously registered full versions.
Only after a new start of High Sierra, the original MAC address was displayed, which is also displayed in the older systems.
We therefore recommend – if the start dialog with the info “Unregistered full version” appears in nessViewer – to restart the computer again.