Some hosts missing username, model, processor or serial number

Hey Guys,
I'm having an issue with the Network Scanner. It works for some of the computers - it shows all the data I want, hostname, username, model, processor, serial number, etc. But for others, it will only show the hostname and the MAC address. For some, it only shows the hostname, MAC address, and the username. Do we know what services need to be running for this program to work? Any hints on what might be blocking it?

It could be virtually anything, but often a firewall or more likely a lack of privileges (Windows 7 and higher have tighter default security settings). If you have some networking experience, launch WireShark and see what responses the network scanner receives (if it receives anything at all).