Multisite not activating in new WP installation

Hi
New to the forum and to multisite functionality.

I've followed the manual, uploaded WP3.01 to my root directory and everything is fine. I opened the wp-config.php file and added the line given between the two existing lines (shown in a cut and paste below)

define('WP_DEBUG', false);
define(‘WP_ALLOW_MULTISITE’, true);

/* That's all, stop editing! Happy blogging. */

I have uploaded the revised file but I don't get 'networks' appearing under tools.

Have I been extraordinarily thick and missed a step?

I'd appreciate anyone's thoughts on this.
Many thanks

Donetta