Express not always accepting credit card only transactions

My customers implementation makes use of PayPal express. The paypal account seems correctly setup to accept pure credit card transactions - meaning no need for paypal account. From Zencart checkout we do redirect to correct paypal url. We can select pay by credit card or pay by paypal account from this location. But if we choose the pay by credit card option, it sometimes loops saying the credit card is invalid when in fact we know for certain the credit card is valid.

Paypal indicated I needed to use their button creation tool to resolve which seems weird to me as I am successfully getting to the site and paypal transactions work as required.

anyone have suggestions on an approach to resolve this?

Please click Reply below and answer all the questions in the Posting Tips section, especially the ones that tell us about your site, software, version, addons, etc.
In addition, will need to see debug logs to know what response is coming back from PayPal in order to determine what the problem is.
http://www.zen-cart.com/showthread.php?61199-Debug-Logging-PayPal

And you're right: PayPal's button-generation tool is completely irrelevant here. In fact it's irrelevant for Express Checkout in general.