Zencart 1.3.8a

Commerce on all of my sites has stopped. 2 Customers called in and said they were getting this message, so I got their credit card info and tried it myself.

Checkout goes just like normal, then when I enter CC and phone number at PayPal and click "Review and Continue" I get this message.

The card you entered cannot be used for this payment. Please enter a different credit or debit card number.
tried two different sites and two different customer accounts and credit cards.

We have not processed an order in over a week.

The only payment method active is "Paypal Express Checkout" and "Zen Free Charge Card"

Made NO Changes, no upgrades, nothing different and all sites have been working swell for years.

HELP