Add New Users Plugin Problem

I am trying to install the Add New Users Plugin. I installed it in the mu-plugins directory but I am getting an error in wordpress...Fatal error: Call to undefined function is_supporter() in /home/sportz22/public_html/powermediallc.org/wp-content/mu-plugins/add-new-users.php on line 154...Line 154 seems to reference something about supporters.

Thanks