Is libclntsh.so where it is expected to be? If the path to the Oracle libraries has changed (includes version number) has that been reflected in your library path?
You can check what's happening using ldd /opt/info1tools/lib/perl5/site_perl/5.8.8/aix/auto/DBD/Oracle/Oracle.so. This will show what libraries are found against the Perl library file. If not found you can try export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:<path to Oracle libs>. When using instant client we have found we have sometimes needed to create links to the instant library directory for sub directories like lib. e.g. ln -s <instant client dir> <instant client dir>/lib
One thing we have in some of our Oracle Perl scripts is at startup we check for Oracle environment and if not set we set that up then exec the script over itself. Maybe not the best way but it does work both from command line/shell and cron.
