Work with phpBB3/WP-United

Okay.. The answer is… It doesn’t work…

I’m getting:

Fatal error: Call to undefined function wp_delete_user() in /wp-content/plugins/wp-united/plugin-main.php on line 854

Where context around this line (with wp_delete_user) is:

$result = wpu_validate_new_user($user->user_login, $user->user_email , $errors);

if($result !== false) {
	// An error occurred validating the new WP user, remove the user.

	wp_delete_user($userID,  0);
	$message = '<h1>' . __('Error:', 'wp-united') . '</h1>';
	$message .= '<p>' . implode('</p><p>', $errors->get_error_messages()) . '</p><p>';
	$message .= __('Please go back and try again, or contact an administrator if you keep seeing this error.', 'wp-united') . '</p>';
	wp_die($message);
	exit();
} else {
	// create new integrated user in phpBB to match
	$phpbbID = wpu_create_phpbb_user($userID);
	$justCreatedUser = $userID;
	wpu_sync_profiles($user, $phpbbForum->get_userdata('', $phpbbID), 'sync');
}

Any idea on what the problem is? I’m able to add a user manually without a problem.