Here are the values from the private notes of the order:

8/20/2008 11:19:29 AM
Credit Card Charge Payment Error:
PayPal Payment Charge Failed. 10505 - This transaction cannot be processed.

8/20/2008 11:19:29 AM
Oops, an error occurred when trying to charge credit card payment

FYI: This just cost me an order.

Alicommerce:

PayPal Payment Charge Failed. 10505 - This transaction cannot be processed.

I cant find anything relevant in the site log.

Go to Admin > Event Viewer and see what paypal related messages are there.

I cant find anything relevant in the site log.

In store admin, go to Tools > Event Viewer and check what's logged.

PayPal Payment Charge Failed. 10505 - This transaction cannot be processed.

Ok, this is what I found out on paypal website:

10505 - The transaction was refused because the AVS response returned the value of N, and the merchant account is not able to accept such transactions.

AVS failed because the billing address the customer entered doesn't match the billing address of the card. Unfortunately it seems that there is no way you can turn this option off in paypal pro. I think there is an option for this verification in other payment gateways like authorize.net.

@cliff

This is by design.

If a payment fails, the order will be marked as unpaid. Then the store owner has to contact the customer for alternate payment method.