An easily made, but just as easily fixed, error can occur when you set up a new payment method in the Newtek shopping cart (and possibly other carts as well). Put simply, if you put "https://" in front of the communication path with your payment provider, and you've already set the communication "protocol" to HTTPS earlier in the setup, you will get the following error:
"Error reading Card
To correct this, make sure you input the URL for the gateway provider without any "http://" or "https://":
The above is from the payment method setup in the Newtek shopping cart, but it is just as applicable with other shopping carts.