Halo Friends

I set up a paypal account for nopcommerce 1.20 using paypal direct and i enabled paypal express also for that and i kept primary currency as usdollar .

          

                   In administration i gave my pay pal account details  username and password  but when i tried to make a payment from user side i am getting error as API Account Password is empty  what may be the reason for this should i make any change in program or wht sought of details should i enter exactly means which password I need to enter for that ...when i opened my business account