SP2-1503: Unable to initialize Oracle call interface

Issue: In one my environment where multiple databases of different versions(9i, 10gR2, 11gR1, 11gR2) are running simultaneously, after I have set the ORACLE_HOME & PATH variables I received the below error while logging into the server.

oracle@linux01=> export ORACLE_HOME=/u01/app/oracle/product/11.1.0.7.0
oracle@linux01=> export PATH=$ORACLE_HOME/bin:$PATH
oracle@linux01=> sqlplus sys as sysdba

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

Solution: After carefully analyzing the environment variables(initial troubleshooting), I observed that the LD_LIBRARY_PATH variable was pointing to a different Oracle Home. Corrected that and was successfully able to login to the database.

Previous Value:
oracle@linux01=> echo $LD_LIBRARY_PATH
/u01/app/oracle/product/11.2.0.3.0/lib

Setting to correct value:
oracle@linux01=> export LD_LIBRARY_PATH=/u01/app/oracle/product/11.1.0.7.0/lib

After Modifying:
oracle@linux01=> echo $LD_LIBRARY_PATH
/u01/app/oracle/product/11.1.0.7.0/lib