The previous tips are helpful, but are the wrong way to approach this. This is EXTREMELY simple to accomplish.
Since I'm not sure if you've messed anything up with your fields, I recommend you create a NEW Guest Self-Reg and set it up the way you want it. Do not hide anything on the receipt page, do not modify the receipt page fields. Keep it simple.
Then, all you need to do is add this to your FOOTER HTML on your RECEIPT PAGE:
<script type="text/javascript"><!--{literal}
addLoadEvent(function() {
Nwa_SubmitForm(_form_name,"ID_"+_form_name+"_submit");
});
//-->
{/literal}</script>
That code is for an IMMEDIATE form submission.
(Do NOT add the meta redirect code!)
Let ClearPass take care of your redirect URL -- the code above will submit the form and ClearPass will redirect to the URL you specify here:
CPGuest > Config > Pages > Guest Self-Reg > (Edit yours) > Advanced Editor > Default Destination
Full tutorial @ https://arubapedia.arubanetworks.com/afp/index.php/How-to:_Auto_Submit_Amigopod_Receipt
Give that a shot and report back,
-Harry