PHP Error for Pro-Sites Paypal Express

Fatal error: Call to a member function get_error_message() on a non-object in /home/eslwebpo/public_html/wp-content/plugins/pro-sites/pro-sites-files/gateways/gateway-paypal-express-pro.php on line 2127.

My paypal test info worked well with S2 member but now I'm using Pro-Sites only. Got this error on first testing. Any ideas? Thanks.