I have ran my Zen Cart store for several years, haven't changed anything and a customer called me this afternoon and told me they can't finish the checkout process. They get to the payment area, go through the steps, put in the credit card information, click on it and it says go to step 2/3 and put information again. I tried myself, thought maybe it was an issue with Authorize.net, so I tried the PayPal option, same thing, it won't click through to finalize payment.

Can someone help me please, I don't know if I should call my hosting company, authorize.net or is this something I need to address in Zen Cart.

I'm running 1.5.5f