osTicket 1.8+ requires PHP 5.3+ if thats what you mean.
You should have an error in your PHP error logs you should go take a look.
Alternatively you can turn on error displaying using these directions:
http://www.tmib.net/osticket-v19x-frequently-asked-questions-faq#2
Either should give us a better idea of what going on.
PHP Fatal error: Call to a member function getId() on a non-object in /var/www/support/include/staff/departments.inc.php on line 72