[Plugin: Fast Secure Contact Form] Problem with Constant Contact option

I cannot get the Constant Contact module to work with Fast Secure Contact Forms. What I am trying to do is email the form to the site admin, email an autoresponder message to the sender, and add the sender email address to Constant Contact. The autoresponder and email to admin work fine until I activate the Constant Contact option.

Then actually the Constant Contact part of it “works” (i.e. the person gets signed up to the selected mailing list) – but then nothing else works. Rather than refreshing with a “thank you” message, the form just refreshes to a blank page with a “1” on it. Neither the autoresponder nor the email to admin get sent.

The site is currently under construction and in maintenance mode so I can’t provide a link.

http://wordpress.org/support/plugin/si-contact-form