Have you tried setting: negotiateServiceCredential="false" As per this earlier thread with a similar problem: http://social.msdn.microsoft.com/Forums/en/wcf/thread/6303a562-96e4-4d5a-be7d-2fb98be8ed4d Here are some relevant MSDN articles which describe WCF troubleshooting and setup: Things to Consider When Implementing a Load Balancer with WCF WCF Troubleshooting Quickstart

Have you tried setting: negotiateServiceCredential="false" As per this earlier thread with a similar problem: http://social.msdn.microsoft.com/Forums/en/wcf/thread/6303a562-96e4-4d5a-be7d-2fb98be8ed4d Here are some relevant MSDN articles which describe WCF troubleshooting and setup: Things to Consider When Implementing a Load Balancer with WCF WCF Troubleshooting Quickstart

There is 5 application servers with IIS hosting WCF application. This WCF application must send requests to one network service. Application servers are in NLB cluster. When I run .svc files locally in application servers, it's completes correctly. When I run request to farm, it throws a error with frequency equal 1 error to ~10 successful requests: System.ServiceModel.FaultException: The security context token is expired or is not valid. The message was not processed. When I drainstop up to 3 application servers in farm, this error never appears even within 100-200 requests. But when I return that nodes online, it appears again. More nodes in NLB cluser = more frequent error events. I used a network sniffer, the error can appear in any host, just in random. Instead of (SYN) packets in start of handshake with network service, application sends (FIN, ACK). But actually this does not give any useful troubleshooting information. Help me, please, I don't know where to dig now.