Problem with Single-Sign-On

Hello,

I have a problem with the integration of SSO. Via the Plug-In “Active Directory Integration” I realize a authentication the Login over our Active Directory. Now I want to integrate a SSO, but it doesn´t work.
In this Community I´ve read how it can be implemented:
http://wordpress.org/support/topic/how-to-create-a-single-sign-on

With this function in the Theme:

function d25_after_setup_theme() {
	// Single Sign On
	if ( !is_user_logged_in() && !empty($_SERVER['REMOTE_USER']) ) {
		$user = wp_signon(); 	// authorization in active-directory-integration
		if ( !is_wp_error($user) ) wp_set_current_user($user->ID, $user->user_login);
	}
}
add_action('after_setup_theme', 'd25_after_setup_theme' );

Could anybody help me with this?

Best regards
Andy