With the new version of BuddyPress out, (1.6), there is no more side menu dedicated for it. So, when WP-invites recognizes that you have BuddyPress, it tries to add a submenu to a nonexistent menu. This plugin is very outdated, and I encourage the developer (Jehy) to update their code likewise:
Go to your /wp-content/plugins/wp-invites/wp-invites.php file and find the line function invites_add_admin_menu()
.
Then, replace it with:
function invites_add_admin_menu()
{
global $wpdb, $bp;
if ( is_site_admin() )
add_submenu_page('plugins.php','WP-invites','WP-invites',8,"manage_invites",'invites_admin');
}
Watch those brackets.
Good luck with your work!
http://wordpress.org/extend/plugins/wp-invites/