It has literally taken me days to figure out my specific issue for my specific setup. First the setup.
Runnint a Server 2012 Standard domain controller with Group Policy and Hyper-V.
In AD DS some users are set up to only be allowed logon to specific computers both locally and remotely via RDP.
The Hyper-V is running a Windows 10 Pro virtual machine also joined to the domain.
Then I have another box with Server 2008 R2 that is a member server jointed to the domain. This box is running NPS and is also set up as the RD Gateway server.
Only users that are allowed to log on to specific computers locally, can also do so remotely via RDP.
When remoting in to VM01 from either the 2012 or 2008 server systems, it was no problem. However, when they tried to remote in from their home computer, the following error was generated.
An authentication error has occurred. The local security policy can not be contacted
There's no way I'm undoing the requirement for Network Level Communication. So I dug, and I dug, and I dug. I finally found the gold at the bottom of this hole.
The solution for my specific situation was to go into AD DS and add the name of the remote computer to the list of computers the user is authorized to log on to. It doesn't matter that the computer they are connecting from is not on the
domain and is sitting in their living room at their house 30 miles away. Their domain login has to be authorized to log on to their personal computer at their house - even though of course, it never will. So if they try to remotely log in from another
computer, they can't. If they get a new computer and it does not have the same network name as their old computer, then they can not connect to their domain computer at work over the internet via RDP with Network Level Authentication.
Of course, there is another option that for me I won't use. It's to allow the user to log on to any computer.