When I try to register, I get a reply saying my serial number is already in use?

First of all, please make sure that you have entered the number - it's easy to enter the wrong number by mistake. Alternatively, could it be that you have previously registered this license number to another user account? If you've lost track of your password you can use the password help on the login page. Submit the email address you used when registering your account, and details of how to reset your password will be sent there. If you no longer have access to that email account, please send us the full postal address and phone number you used when registering that user account, and we will investigate further.