Dear Nick, sorry for the late reply. Just some more info, we have 2 NPS servers, one windows 2008 (10.32.192.16) and one Windows 2012R2 (10.32.192.17). They both use the same certificate. When i stop the NPS service on the windows 2008 server, authentication is not working, So the problem is that the 2012 R2 NPS server is not answering. Can I send you some more info by email ?