Adding a new user

I’m slightly modifying a plugin that allows people to ‘subscribe’ by entering their Name and email into a form. This data is then used to create a subscriber-level user in the wordpress users database.

I’ve used the following code to acheive this.

$user_pass = substr( md5( uniqid( microtime() ) ), 0, 7);

$user_id = wp_create_user( $user_login, $user_pass, $user_email );

$user = new WP_User($user_id);
$user->set_role('subscriber');
wp_insert_user( array ('ID' => $user_id, 'first_name' => $userName) ) ;

It basically sets the username as the first part of the email address, generates a random password. The problem I’m having is setting the first name as the name they entered ($userName is defined as what the person subscribing typed in as their name). It all works except the bit adding the first name. Currently the wp_insert_user() function just doesn’t do anything.