I get the following error when trying to save the settings:
Fatal error: Call to undefined function get_current_screen() in \wp-admin\includes\class-wp-posts-list-table.php on line 255
The get_current_screen has been deprecated in WP 3.3. I noticed that you say this plugin is compatible up to WP 3.2.1. I have verified that and it seems to work fine in that version.
I just wanted to alert you to the error as the new WP 3.3. will be released soon.