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
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(DESCRIPTION=(DESCRIPTION=<br />
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>