11gR2 SP2-1503: Unable to initialize Oracle call interface

$ which sqlplus
/oracle/system1/db/tech_st/11.2.0/bin/sqlplus
ibes01@system1: sqlplus
SP2-1503: Unable to initialize Oracle call interface
SP2-0152: ORACLE may not be functioning properly
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The cause is that the variable ORA_TZFILE was pointing to a 10g environment.
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$ set | grep TZ
ORA_TZFILE=/oracle/system1/db/tech_st/10.2.0/oracore/zoneinfo/timezlrg.dat
TZ=MET-1METDST

$ unset ORA_TZFILE
$ sqlplus

SQL*Plus: Release 11.2.0.1.0 Production on Tue Aug 24 08:58:55 2010

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