Just to let you know on line 26 you are using the older level based system which was depreciated in version 2.0 of wordpress, it would be worth while switching over to the roles & capabilities system, a simple fix would be this:
Notice: has_cap was called with an argument that is deprecated since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /wp-includes/functions.php on line 3321
Perhaps you would push out a point release for everyone...
add_submenu_page('ms-admin.php', 'User Activation Keys', 'User Activation Keys', 'edit_users', 'act_keys', 'ds_delete_stale');