hi all from time to time we have problem with authentication. Client boot, logon screen is shown but no network is available. We use NAP with certificates. After logon and restart dot3svc it works. client has symantec antivirus with firewall. If we use MAC Address authentication without certificat it works client: Windows XP SP3 Server: Windows Server 2008 R2 Cisco Chris

Hello, Thank you for your question. I am trying to involve someone familiar with this topic to further look at this issue. There might be some time delay. Appreciate your patience. Thank you for your understanding and support. Regards,Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Have you given this a chance? are the symptoms/behavior matching? http://technet.microsoft.com/en-us/library/dd348450(WS.10).aspx Ketan Thakkar | Microsoft Online Community Support