Double Duty MailChimp Form Not Working

I am having problems getting a contact form to work as a double duty form with MailChimp. The form submits OK and the message comes through to my email, but nothing happens with MailChimp.

I am getting this message in my debug report:

Array
(
    [type] => 8
    [message] => Undefined variable: email
    [file] => /home/mysite/public_html/cms/addons/apps/perch_mailchimp/PerchMailchimp_Subscribers.class.php
    [line] => 62
)