PATH variable was pointing to ORACLE_HOME rather than ORACLE_HOME during the upgrade. Hence, the wrong version of sqlplus was invoked



sqlplus banner follows (note that sqlplus release is whereas the database version is


$ sqlplus / as sysdba
SQL*Plus: Release Production on Mon Aug 15 21:10:55 2011
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Connected to:
Oracle Database 11g Release - 64bit Production
Connected to an idle instance.