You should really have a look into sharing model in local security policies of those Windows XP computers that cannot be scanned. In my experience, that's the most common reason: http://www.clearapps.com/help.html#faqa1 (solution #4)

Thanks, that helped as I discovered there were several machines not scanning and now only two are not scanning. Secpol is set correctly on these last two machines, they are correctly identified when I do the scan but get stuck on connecting to CIM namespace and then finally "node couldn' be scanned with any known method. Check your password, which I know is correct. I have two admin accounts on these machines and tried them both, Firewall is off. Do I need to have certain ports available? I do have a hardware firewall but I think we have allowed for this software in the Hardware firewall, but just to be sure what ports are needed?

Hello,

Please check the solutions available here once again: http://www.clearapps.com/help.html#faqa1

If the problem persists, please, try to disable the firewall temporarily.

To scan using auto-deploying agent utility, please open the ports: TCP 22, UDP 137, TCP 139.

To scan via WMI, please open the ports: UDP 137, TCP 22, TCP 139, UDP 138, TCP 135, TCP 1051.

I have researched this issue before with no luck.....I have 2 notebooks with Windows 7 on them, one Professional on Ultimate, sometimes they can see our Windows 2003 SBE Server just fine along with other computers on the network...other times they can't see anything but themselves.,
The only work around I have found for this is to install Windows XP Mode and use that, technically not a practical solution but something that works for the time being. Right now I can ping and access the files on this notebook just fine from an XP machine but I can not see the XP machine for this notebook.
All computers are on the same Workgroup (Not a HomeGroup), all can access the internet just fine, printers are directly connected to the network and can print just fine but not access folders on individual computers or Servers. All firewalls are disabled ie Avast and Windows. Still nothing. Even though it doesn't work right now, tomorrow it might work just fine without changing anything. Other times the Windows 7 machine can see the computers but not access the files. This is such a common issue that if you were to Google it, it would pop up under suggestions??? Can anyone help??????

How is this related to Network Inventory Advisor?