W3 Total Cache Problem

I’m trying to install this plugin, but when I activate it, I get this fatal error: “wp-config.php could not be written, please edit config and add: define(‘WP_CACHE’, true); before require_once(ABSPATH . wp-settings.php’);

So I update wp-config.php with that line, and it kills the site. It just white screens. I remove it and everything’s fine.

Any suggestions?