Marketpress using and Paypal Problems

I have set up my and paypal information in my payment tab. When I try to test I get "There was a problem finalizing your purchase. (TESTMODE) The merchant login ID or password is invalid or the account is inactive. Please go back and try again." When I test PayPal I get "There was a problem connecting to PayPal to setup your purchase. Please try again.
10002 - Security error - Security header is not valid" I have triple checked all the user id's and passwords etc but I still get the messages.