Strange issue... the plugin does work for the main site of the network but not for the child sites of the network. It sometimes just redirects to the plugins option page of the main site. Anyhow, the 2 options don't get saved into the options table for the child site.
Humm... should have looked at the other posts first (time to go to bed I guess)... issue is already around since WP 3.0. See http://wordpress.org/support/topic/members-only-options-not-saving-for-multisite-30-blog?replies=4 for the solution. Hopefully it gets included in the next update of the plugin.
<form method="post" action="<?php echo $_SERVER['PHP_SELF'] . '?page=' . basename(__FILE__); ?>&updated=true">
should be replaced with:
<form method="post" action="<?php echo 'options-general.php?page=' . basename(__FILE__); ?>&updated=true">