I have Contact Form 7 for Constant Contact (not sure which plugin is which ) and I have a 2 line sign-up form (Full Name and EMail Address). But, when I sign up for the list, I get the red box message that says "Failed to send your message...". That said, I did get a confirmation back from Constant Contact, so I think the problem is sending the e-mail from Contact Form 7 to the user, not the handshake with Constant Contact.
I added the akismet tags to the e-mail and name fields, but it didn't help. The site is http://www.globalnetworkatl.com - can you point me in the right direction to solve this problem?