Cannot register product

I cannot register my copy of Scrivener. I have the serial number and my name, and it will say Validation Successful! Thank you!" and then immediately after that I get the following error:

Invalid serial number and/or unsername
Please register the serial number and name to match your order confirmation email.
One or the other is blank when retrieved from the registry.

How do I fix this so I can register my copy of scrivener?