The form on the checkout page has been edited to 1) use recortdset info as the values, but the recordset is not returning a reszult, and 2) Submit on page load.
this is causing the validation on the confirm page to fail in an endless loop, becuase it redirects to checkout which submits on load, fails, redirects, submits, fails etc..
the recordset is set to filter using the UserID session variable, but your login creates a session named:
use that session instead. and be careful when submitting a form on page load.