Hi I recently joined a new coy and inherited a long running issue :(. The issue is we have an in-house application that our external clients log onto. We have noticed that for some time now, when they logon, they get this error message "Security check failed during service call". To fix this issue temporary, we have to recycle the application pool serving this site. When I check the event logs on the web server, I see the following errors logged: 1. Event ID: 1054 Message: The processing of Group Policy failed. Windows could not obtain the name of a domain controller. This could be caused by a name resolution failure. Verify your Domain Name System (DNS) is configured and working correctly. 2. Event ID: 5011 Message: A process serving application pool 'xxxx' suffered a fatal communication error with the Windows Process Activation Service. The process id was '8162'. The data field contains the error number. 3. Event ID: 5719 Message: This computer was not able to set up a secure session with a domain controller in domain XXXX due to the following: The RPC server is unavailable. This may lead to authentication problems. Make sure that this computer is connected to the network. If the problem persists, please contact your domain administrator. I have checked the health of the AD and DNS and all results are pass. Can anyone help with this sort of issue. ThanksIsaac2k2