I'm using PP IPN and running Zen 1.3.6 so no PayPal patch installed. Here's the glitch I'm having:

From checkout, the customer proceeds to the PayPal page and selects:

Don't have a PayPal Account?

Use your credit card or bank account (where available).
They enter their information but receive the following error message after attempting to proceed:

The email address or credit card has already been added to a PayPal account. If you have already opened a PayPal account, enter your email address and password into PayPal Checkout and click Log In. Otherwise, enter a different email address or credit card number to complete your purchase.
However, the email address and credit card have not been added to a PayPal account. This is happening with a live card, not in the sandbox.

Any idea what this may mean?

Thanks!