The ORACLE_HOME environment variable was already set. This prevents proper use of multiple Oracle homes and, as it is not required for any Oracle products to function, it will be unset in your environment.
The ORACLE_HOME environment variable will be unset automatically.
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Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/dbinstaller_errormessages.htm