It is not possible for people to help you based on the little info you've given. First of all, we can't see the C5 UI because we're not logged in users on your site. Second, I don't see a form on the page you linked to.

If you know it's related to some HTML you pasted into the HTML block, you should look through that code yourself first to see if you can spot any obvious errors. If you can't find it yourself, try pasting that code here in the forums (inside a code tag -- see little instructions beneath the forum message text area).