Issue with Website Membership

Hi. I've set up a membership login/register form here: http://www.vaccinelearningzone.com/login/signup.php

When you hit submit, you get the following error:

Notice: Undefined variable: errors in /content/Hosting/v/a/vaccinelearningzone.com/web/login/user-signup.php on line 90 Mail Error:

which equates to this line:

if ($mailErrors) { die("Mail Error: $errors"); }

from this section:

// send message
$emailTemplate = "/emails/new_signup.php";
$emailHeaders = emailTemplate_load(array(
'template' => websiteLogin_pluginDir() . "/$emailTemplate",
'subject' => '', // set in template
'from' => '', // set in template
'to' => $_REQUEST['email'],
'placeholders' => array(
'username' => array_key_exists('username', $_REQUEST) ? $_REQUEST['username'] : $_REQUEST['email'], // if using email as username then show that instead
'password' => $password,
'loginUrl' => "http://" . $_SERVER['HTTP_HOST'] . $GLOBALS['WEBSITE_LOGIN_LOGIN_FORM_URL'],
),
));
$mailErrors = sendMessage($emailHeaders);
if ($mailErrors) { die("Mail Error: $errors"); }

As far as I can tell, I've got all the paths correct, haven't deleted anything important and the file http://www.vaccinelearningzone.com/cms/plugins/emails/new_signup.php is functioning correctly.

The account gets created, the registration confirmation email gets sent, but this error prevents going on to the post login URL.

Do you have any ideas what's going wrong?