Radio Button Javascript

I have a form  with a radio button (and of course other fields).

The form statement:

<form method="POST" action="http://www.rain1.com/new-site/authorize_net.php" name="st" onSubmit="return validate_pmnt_form();">

The radio button:

Please note:  Service packages are non refundable and non transferable.&nbsp;&nbsp; <input type="radio" name="ntr" value="y" style="visibility; visible;">&nbsp;&nbsp;  Click to indicate you have read this statement.

The javascript (in function validate_pmnt_form)

if (!document.st.ntr[0].checked) {
      alert("Please click that you understand the non-refundable & non-transferrable statement.");
                        return false;
                  }
If you DO NOT click the radio button, it still submits the form.

What's wrong?

Thanks