The security context token is expired or is not valid

I am facing below issue while calling _service.update(entityObj);

Unhandled Exception: System.ServiceModel.Security.MessageSecurityException: An unsecured or incorrectly secured fault was received from the other party. See the inner FaultException for the fault code and detail. ---> System.ServiceModel.FaultException: The security context token is expired or is not valid. The message was not processed.     --- End of inner exception stack trace ---   

Code:

 private static void RefreshService()
        {
            try
            {
                string orgServiceUrl = Default.CRMServiceUrl;
                Uri organizationUri = new Uri(orgServiceUrl);
                Uri homeRealmUri = null;
                ClientCredentials credentials = new ClientCredentials();
                credentials.Windows.ClientCredential = CredentialCache.DefaultNetworkCredentials;

                OrganizationServiceProxy orgProxy = new OrganizationServiceProxy(organizationUri, homeRealmUri, credentials, null);
                orgProxy.Timeout = new TimeSpan(1, 0, 0);
                _service = (IOrganizationService)orgProxy;
            }         
            catch (Exception)
            {
                throw;
            }
        }