ConstantContact integration with Membership Subscription Form

I installed the Constant Contact Wordpress Plugin which gives me an option to integrate a checkbox in my subscription form that, when checked, will automatically sign anyone who registers for any of my subscription plans to my e-Mail list at ConstantContant.
I activated that option and went through the process to test it as a new subscriber to my site.
The checkbox is available within the subscription form and I checked the box on new user registration form, but it did not successfully add my e-Mail as a new user of the site to my ConstantContact contact list as it is supposed to.

I contacted ConstantContact, but since it is a third-party plugin, they do not offer any support for it. So I attempted to find something from the plugin developer, but they said I actually have to contact WPMU and request support for this issue.

Can anyone help??
I would greatly appreciate it!