Had WP_DEBUG enabled and these popped up.
On plugin activation:
The plugin generated 486 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.
On page: index.php?page=secure_invite and dashboard widget on index.php:
Notice: WP_User->id was called with an argument that is deprecated since version 2.1! Use WP_User->ID instead. in /wp-includes/functions.php on line 3551 Unlimited invites