[ora1@RHEL1 ~]$ sqlplus
sqlplus: error while loading shared libraries: libsqlplus.so: cannot open shared object file: No such file or directory
[ora1@RHEL1 ~]$

i believe that this error comes when u r running sqlplus from user other than oracle. for this (10.2.0.1) you have to run following script and that is included in Patch 4516865

put both files in $ORACLE_HOME/install/ directory.
n
1. cd $ORACLE_HOME/install
2. Run changePerm.sh script.

then press y