The WordPress cache system is not enabled! Please, activate it adding…

I’m getting the following error when I activate Hyper Cache:

The WordPress cache system is not enabled! Please, activate it adding the line of code
define("WP_CACHE", true);
in the file wp-config.php just after the define("WPLANG", ...).

For now, I’ve just de-activated the plugin until I’m certain on how to proceed. It seems to me this error should not occur.