This may well be a PHP version problem -- 4.2.1 is very old and probably a bit risky to run security-wise -- but please double-check to make sure that lib/smarty/Smarty.class.php is free of typos. If you've modified OJS, you might have introduced a typo in another file that's going unnoticed until Smarty.class.php is loaded. (Since other Smarty-using pages are working fine, that's not unlikely.)
FYI, you can run the upgrade script via the web interface -- turn "installed" to "Off" in config.inc.php and follow the upgrade link. Make sure your php.ini execution timeouts are generous, as the upgrade can take a while.
In any case, I'd suggest upgrading to the newest 4.x PHP ASAP; that'll probably solve the issue for you, and you'll have a much safer system too. In the meantime, OJS 2.0.0 is probably fine for your needs, but make sure that you've applied this patch
Open Journal Systems Team
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