When you establish an https connection WAS will use either the certificates in cacerts or DummyServerKeyFile.jks as the client certificates for authentication. It is likely that whichever of these is being used contains an expired certificate. It is also possible the trust store contains an expired certificate, the exception would be thrown in that case too. Check those keystores and remove or update the expired certs. IBM has patches to do this for you I believe.
-Z
