I cannot get this to work with the Constant Contact addon. The form itself works great. However, when I activate the Constant Contact addon plugin and submit a form, I get a blank screen with just a number 1 on it, the autoresponder message is not sent nor is the form submission sent to the admin email. I do get signed up on the Constant Contact mailing list, so as far as that part of it goes it is "working". I also posted this on the Constant Contact plugin page as I don't know where the problem lies.
The site is under construction and in maintenance mode so I can't provide a link. I did try taking it out of maintenance mode for a minute to test and the same thing happened.