[Plugin: Admin-Colour] Error when activated..

Warning: Cannot modify header information – headers already sent by (output started at /home/sitename/public_html/sitename/wp-content/plugins/admin-colour/Admin-Colour.php:47) in /home/sitename/public_html/sitename/wp-includes/functions.php on line 861

wordpress 3.2.1 multisite..

http://wordpress.org/extend/plugins/admin-colour/