Recently I encountered a strange error where I couldn’t install Network Policy Server from the Server Manager.
Rather than fight with Server Manager, I punted and installed it via PowerShell. The installation that way worked without an problem.
Run PowerShell as Administrator
The name of the feature has changed from “npas-policy-server” to just “npas”. For newer versions of Windows Server, run:
install-windowsfeature -name npas -IncludeManagementTools
Older (probably unsupported) versions of Window Server would use:
install-windowsfeature -name npas-policy-server -IncludeManagementTools