In my Windows Server 2008 R2 OS in the Event Viewer there is an error pertains as Microsoft-Windows-Network Access Protection Error ID 21 states-(The Network Access protection agent failed to acquire a certificate for the request with the correlation-id{E91363E5-05C2-4992-82D6-7D2FA2F1DA61}-2011-10-31 05:21:18 474Z from https://win-bnilite1545.mumthaz.contoso.com. The request failed with the error code (2147942487).This server will not be tried again for 10 minutes.contact the HRA Administrator for more information). What is this error? And What is the remedy for this error? - System - Provider [ Name] Microsoft-Windows-NetworkAccessProtection [ Guid] {4EF850D8-BF30-4E64-A917-EE21B9BE1F0A} EventID 21 Version 0 Level 2 Task 0 Opcode 0 Keywords 0x8000000000000000 - TimeCreated [ SystemTime] 2011-10-31T17:17:21.669229100Z EventRecordID 2669 Correlation - Execution [ ProcessID] 416 [ ThreadID] 3196 Channel Microsoft-Windows-NetworkAccessProtection/Operational Computer WIN-BNILITE1545.mumthaz.contoso.com - Security [ UserID] S-1-5-20 - UserData - NapEvent URL https://win-bnilite1545.mumthaz.contoso.com CorrelationId {E91363E5-05C2-4992-82D6-7D2FA2F1DA61} - 2011-10-31 05:21:18.474Z HResult 2147942487 Blackout 10 MumthazMuhsin

Hello, start by that: http://technet.microsoft.com/en-us/library/dd408676(WS.10).aspx More if you ask them here: http://social.technet.microsoft.com/Forums/en-US/winserverNAP/threads This posting is provided "AS IS" with no warranties or guarantees , and confers no rights. Microsoft Student Partner 2010 / 2011 Microsoft Certified Professional Microsoft Certified Systems Administrator: Security Microsoft Certified Systems Engineer: Security Microsoft Certified Technology Specialist: Windows Server 2008 Active Directory, Configuration Microsoft Certified Technology Specialist: Windows Server 2008 Network Infrastructure, Configuration Microsoft Certified Technology Specialist: Windows Server 2008 Applications Infrastructure, Configuration Microsoft Certified Technology Specialist: Windows 7, Configuring Microsoft Certified IT Professional: Enterprise Administrator Microsoft Certified IT Professional: Server Administrator Microsoft Certified Trainer

I realize this question is over a year old now, but I ran into the same problem when playing around with NAP in my lab today, and web searches didn't turn up any other results. In case anyone else comes across this thread with the same issue, the problem is in the URL you're publishing in the Trusted Server Groups. It must be https://<FQDN of HRA>/DomainHRA/hcsrvext.dll (or /NonDomainHRA/hcsrvext.dll for anonymous connections, if you're allowing those). Microsoft's documentation on this topic would greatly benefit from mentioning that, or at least including a sample URL.