there are a number of things i see wrong with the way this form is set up.
first, the number one rule when working with forms is to understand that all form processing _must_ happen on the forms action page.
in this case, the form tag:
<form class="Basic_Default" id="ultra_Basic_Default" name="ultra_Basic_Default" method="post" action="thanks.php">
has the action set to the thanks.php page:
this means that any server behaviors that process the form need to be on that page.
the Universal email behavior is correctly on that page, but you have added the server validation to the form page.
The server validation must be on the action page in order for it to work
also, you mention that the captcha validation does not work, but there is no captcha validation applied.
the server validation only has one setting in it, the like entry setting for the email address.
I would suggest recreating the form using form builder, leave the action to it's default setting which will be to post to itself.
In the form builder settings, you add the like entry for the email address and the captcha to have those automatically added to the page.
after the age has been created, you can edit the UE server behavior to change the redirect so that it goes to the thank you page after sending the email.