Paypal Intergration / Paypal Payments Pro Fix

I need a fix to the payment system which has stopped working today. It is a paypal website pro system which has been installed on our website. It continues to work on a sister website and stopped working on the other one. Thus, the solution should be simple and will take a few minutes to fix with a qualified specialist. The second phase of this is new installation on a new website. The script is ready, along with a new paypal account so it is a simple job of moving the script and configuring it to the new account. Specialist can do this in about 30 minutes time. This is a RUSH project.