If there is no issue for tns entries ,The next thing in a RAC configuration i will verify is the LOCAL_LISTENER and REMOTE_LISTENER settings.I have seen issues where this error is reported for incorrect LOCAL_LISTENER and REMOTE_LISTENER settings.
Why are there two entries for Description in tns entry
You have mentioned that this entries are mentioned in alert log. Have you checked the client from which it is coming. Also as Suvv sugested try checking local_listener and remote_listener value. Note that if you are using scan (11gr2), remote_listener should be scanname:<port>