Thin clients are scanned best with SNMP. You might need to enable SNMP directly on the target systems. Afterwards scan them following the instructions in
this article.
In case you are scanning network devices which don't provide any of the protocols mentioned
here, you could enable "Save Ping IP" under
Configuration\Scanning methods, section
IP Address Range scanning. This causes Lansweeper to generate an asset page for devices which only replied to ping.