Moving wp-content folder

Hi all
I’ve been running wp ok but now I want the wp-content folder moved out of my ‘blog’ folder which contains wp-admin & wp-includes.
I followed the instructions on http://codex.wordpress.org/Editing_wp-config.php “Moving wp-content”.
I’m ending up with a blank screen.
Have put in:

define( 'WP_CONTENT_DIR', $_SERVER['DOCUMENT_ROOT'] . '/wp-content' );
define( 'WP_CONTENT_URL', 'http://www.mysite.co.uk/wp-content');
define( 'WP_PLUGIN_URL', 'http://www.mysite.co.uk/wp-content/plugins');

I’ve looked at over 100 forum topics but can’t find anything directly relating to this.
Have I done something stupidly obvious?
Any help would be greatly appreciated.