Error 6 initializing SQL*Plus

When I tried to connect sqlplus was giving an error.

-bash-3.00$ sqlplus '/as sysdba'
Error 6 initializing SQL*Plus
Message file sp1.msb not found
SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory

Log out from the user and login again. Don't source any environment variables yet.
Check the location of your correct oracle home by going into the directory. Export the oracle home

-bash-3.00$ export ORACLE_HOME=/u01/oracle/product/10.2.0/db_1
-bash-3.00$ export PATH=$ORACLE_HOME/bin:$PATH:.

Now try log in again

-bash-3.00$ sqlplus '/as sysdba'

SQL*Plus: Release 10.2.0.1.0 - Production on Sun Jul 6 01:04:52 2014

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> exit