Subscribe2 Plugin | Users Can’t Subscribe Using Form

I just installed and activated the Subscribe2 plugin. In addition I have:
1. A Subscription page with a shortcode of [subscribe2] with a blank line before and after
2. In Subscribe2 > Settings, I have “Send Email From” set to a WP user (Administrator role) that has an e-mail address of [email protected].

When I enter an e-mail address on the Subscription page and click “Subscribe”, I am taken to another page on the site (the About page) with no messages whatsoever. When I check the inbox for the e-mail address I attempted to subscribe there is no confirmation e-mail (yes, I checked junk/spam). When I go to Subscribe2 > Subscribers (checking to see if the new e-mail has been added), all I see are the three originally defined WP user e-mail addresses – but not the new e-mail address I just tried to subscribe.

I’ve read through many forum posts on this but I haven’t come up with a solution.

Please note I’ve also tried this using the default TwentyEleven theme with all other plugins deactivated – same result.

The Subscription page is here: https://audienceavenue.com/test-page-2/

Two other questions…
1. Do users who are attempting to subscribe need to be previoulsy registered on the WP domain for which they are subscribing?
2. I have a test environment set up where the root domain name is mydomain.com/aaa/bbb/ccc. I also have a user set up (Administrator role) with an e-mail address of [email protected]. Will the Subscribe2 plugin function properly even though my root domain is several sub-folders deep?

Thanks.