Your best bet is probably to suppress NOTICE and WARNING error messages, either by modifying the system-wide php.ini, or by adding the appropriate ini_set calls to each OCS PHP script. (See http://ca.php.net/manual/en/function.ini-set.php
for more information on ini_set; error message reporting options are documented in php.ini.)
Alternately, change php.ini so that error messages are re-routed to a log file and not displayed.
OCS is a few years old now, and while it's still perfectly serviceable, PHP has moved on somewhat.
Open Journal Systems Team