Unable to start Express Checkout - checkout with paypal in shopping cart

We are having a problem with how PayPal Express Checkout is functioning. We have the "Pay with PayPal" button showing on the shopping cart. However,when a customer clicks it redirect to paypal page only customer is not logged in but if customer is already logged in then it keeps on cart page and throw error "Unable to start Express Checkout."

I done this change : Enable SSL verification = 'No' but still not working for logged-in customers only.