SP2-1503: Unable to initialize Oracle call interface in Oracle 11g

When we were trying to connect to our upgraded 11.2.0.3 database, below error was thrown and we were not able to connect.

$ sqlplus as sysdba
SP2-1503: Unable to initialize Oracle call interface
SP2-0152: ORACLE may not be functioning properly

Done intial checking :

>> user oracle was in the correct database admin group (/etc/group)
>> No tnsnames issues as TNS_ADMIN variable is poiting to correct directories and all files( tnsnames.ora, sqlnet.ora, listener.ora) in it have valid entries.
>> $PATH variable was pointing to correct $ORACLE_HOME/bin

On checking the environment variable closely, it was found that one of the variable ORA_TZFILE was pointing to non-existent file.

echo $ORA_TZFILE

/u01/oracle/dev/db/tech_st/11.2.0/oracore/zoneinfo/timezlrg.dat

ls -ltr /u01/oracle/dev/db/tech_st/11.2.0/oracore/zoneinfo/timezlrg.dat

ls: /u01/oracle/dev/db/tech_st/11.2.0/oracore/zoneinfo/timezlrg.dat: No such file or directory

This file timezlrg.dat was not present at the location, though there were other files with names like
timezone_<N>.dat.

–

—
-rw-r–r– 1 oradev dba 507957 Aug 18 2011 timezlrg_2.dat
-rw-r–r– 1 oradev dba 493675 Aug 18 2011 timezlrg_1.dat
-rw-r–r– 1 oradev dba 791430 Aug 18 2011 timezlrg_14.dat
-rw-r–r– 1 oradev dba 782475 Aug 18 2011 timezlrg_13.dat
-rw-r–r– 1 oradev dba 785621 Aug 18 2011 timezlrg_12.dat
-rw-r–r– 1 oradev dba 787272 Aug 18 2011 timezlrg_11.dat
-rw-r–r– 1 oradev dba 792894 Aug 18 2011 timezlrg_10.dat
—
–
Unsetting this variable solved our issue.

$ unset ORA_TZFILE

$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Tue Oct 16 11:45:08 2012

Copyright (c) 1982, 2011, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 – 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>
We can also set and use the desired timezone file and if we do not set it then by default it will use maximum value of n.

export ORA_TZFILE=$ORACLE_HOME/oracore/zoneinfo/timezlrg_<N>.dat