guest checkout error

[WHS]

Recently, I try to use AbanteCart in my online store. When I test the guest checkout, an error is occurred if one of three occasions.
Clicking on "CHECKOUT" bottom in main page to go to Checkout page,
Select "GUEST CHECKOUT" then click "Continue" to
GUEST CHECKOUT STEP1, fill in all required info click 'Continue" bottom to
GUEST CHECKOUT STEP 2, there are two payment selections: Papal standard Payment and Paypal Express Payment.
By selecting Paypal Standard Payment, the checkout goes through without problem.
However, with "Paypal Express Checkout" and click "Continue" to get Confirmation page,
after clicking on "CONFIRM ORDER" bottom, an error message shows in a new page as "Paypal Express Checkout Error", Error has occurred during request. Please try again.. Please help!!

If directly click the Checkout with Paypal bottom (for Paypal Express Checkout) on VIEW CART page, the checkout can go through without problem as a guest.

[abolabo]

did you tried to test paypal credentials on paypal express extension's settings page on admin side?

[abolabo]

new version here
http://www.abantecart.com/abantecart-extension-categories/79-payment-methods/114-paypal-express-checkout