Genesis eNews and Mad Mimi

I’ve read many threads about this but still cannot get it resolved. I am trying to use Genesis eNews Extended with my Mad Mimi email sign up form. I have it configured exactly how it shows in the tutorial.

https://madmimi.com/signups/subscribe/(my account)/
signup[email]
signup[firstname]
signup[lastname]

When I test a sign up, I receive this message (it appears on my Mad Mimi sign up page in a new window).

1 error prohibited this webform from being saved

There were problems with the following fields:

Email is invalid

But if I re-enter the info on that page with the error, it goes through fine.

Any insight into resolving this issue would be greatly appreciated! Thank you!

https://wordpress.org/plugins/genesis-enews-extended/