Maintenance mode troubles

hi
I found some simple code to add a maintenance mode page which is placed inside functions.php and it’s working but it causes ALL my pages on website to go into maintenance mode. You see, what I had in mind was to keep my website up but when a user clicks a certain link to redirect to this maintenance mode page (it’s still the same page but it overrides my current page as I noticed in URL)

functions.php I placed:
=======================
/***************************************************************************
* @author: Boutros AbiChedid
* @date: November 14, 2011
* @websites: http://bacsoftwareconsulting.com/ ; http://blueoliveonline.com/
* @description: Function that puts WordPress Website in maintenance mode.
* @tested on: WordPress version 3.2.1 (but it works on earlier versions.)
****************************************************************************/
function activate_maintenance_mode() {
//If the current user is NOT an ‘Administrator’ or NOT ‘Super Admin’ then display Maintenance Page.
if ( !(current_user_can( ‘administrator’ ) || current_user_can( ‘super admin’ ))) {
//Kill WordPress execution and display HTML maintenance message.
wp_die(‘<h1>Website Under Maintenance</h1><p>Hi, our Website is currently undergoing scheduled maintenance.
Please check back very soon.
Sorry for the inconvenience!</p>’, ‘Maintenance Mode’);
}
}
//Hooks the ‘activate_maintenance_mode’ function on to the ‘get_header’ action.
add_action(‘get_header’, ‘activate_maintenance_mode’);

?>