It does look like there is a custom signup form experience on your website. If the signup form is not working, we can definitely help you if it uses the API. To help though, we would need you (or your website admin/developer) to share the following information. Feel free to email that to us at firstname.lastname@example.org as some of it may be account sensitive.
API integration code (looks like you're using ASP, will need the ASP code you use to send requests to the API)
Error message you're receiving when the request fails
Sample email address(es) that the failures are happening for
Looking forward to hearing back from you so we can help get to the bottom of your problems.
Dave Berard Senior Product Manager, Constant Contact