Cold Fusion / Authorize.Net / eCart 4

I have eCart4 and am using it on my Cold Fusion website with [login to view URL] as my gateway.? ? My shopping cart is having 2 main problems, first off most of the time you cannot add more then one item to the cart and secondly about 98% of the people who checkout get errors.? I need this fixed asap!? Users will get through the entire checkout, enter all their info, then come to an error page.? Checkout with PayPal works as far as I know but its the credit cards that are being problematic.? If you want you can see it at [[login to view URL]][1]? even if you want to try going through the check out thats fine, if it actually makes it through I will refund you, but I dont think that will happen.