I am securing a .net web service (framework 2.0) with WSE3 mutualCertificate10Security Assertion. When request are valid all is fine and the response is wellformed, but when the request is invalid (cause a invalid signature, failed check, or soapexception thrown), the web server isn't able to process the response to send to the client. The error in application event log is: An error occured processing an outgoing fault response. Details of the error causing the processing failure: System.InvalidOperationException: Send security filter on the server could not retrieve the operation protection requirements from the operation state. en Microsoft.Web.Services3.Security.SecureConversationServiceSendSecurityFilter.SecureMessage(SoapEnvelope envelope, Security security) en Microsoft.Web.Services3.Security.SendSecurityFilter.ProcessMessage(SoapEnvelope envelope) en Microsoft.Web.Services3.Pipeline.ProcessOutputMessage(SoapEnvelope envelope) en Microsoft.Web.Services3.WseProtocol.GetFilteredResponseEnvelope(SoapEnvelope outputEnvelope) All certificate permissions are OK (when request is OK the web service is able to sign the response). Error occurs only if a soapFault must be returned in the response. Any ideas?