Checkout fails when Authorize.net is activated

-- HikaShop version -- : 2.2.2 Business
-- Joomla version -- : 2.5
-- PHP version -- : 5.3
-- Browser(s) name and version -- : All
-- Error-message(debug-mod must be tuned on) -- : Email address already used. no other messages.

We are using Authorize.net as the payment method and everything works fine in the debug mode. Once that is turned off, the checkout fails. The first problem occurs if a Joomla user tries to login -- it stops them at the registration. The second problem is that if a new user gets past the registration, the coupon code will not show in the price (its a straight 20% discount on each product). This apparently is not a problem for someone outside of our firewall. I did check with our security and nothing is being blocked or flagged. No error codes are appearing. Our login is a guest and using the email/confirmation and address for billing. We have the latest update with the business version. Help please. Thank you very much.

Hi,

We'll need more detail about the issue that you are having, can you give us more information like :
1. Some screenshots of :
- your checkout configuration through "Hikashop->System->Configuration->Checkout"
- your coupon configuration
2. A link to your store for testing purpose.

Thanks.