Hi Dan,
I have seen that when the computers that being browsed/searched have firewalls that block the NST tool's necessary traffic. Test to see if this is the root cause in your case by temporarily opening up UDP port 137 and TCP ports 445 and 139 on the clients. (If the clients have Windows Firewall: enable File and Printer Sharing. That will allow traffic on all the ports NST needs to have open.)
Please do keep this thread up-to-date with your progress!
Thanks and best regards,
Mick