NAP troubleshooting isn't a no-brainer. By its very definition, NAP is meant to keep people out of your network. And discovering why they're out of your network can be difficult. There are several areas you can check to get to the bottom of NAP woes:
Group Policy RSoP
The NPS server configuration
However, before you even jump into logging again, I heartily recommend that you check out the obvious stuff that I already described in the "NAP Clients in a Domain-Joined Environment" section (the same goes for a nondomain joined client):
Ensure that the NAP Service is running on the client.
Do a Quick NAP Agent Status Check (ipconfig /all).
Do a Quick NAP Enforcement client check.
Do a Quick NAP ...