Hello,
thank you for your feedback!
We are sorry for the inconvenience.
If your serial number was generated after 1 October 2012 you should be able to upgrade Revo Uninstaller Pro to version 3.0 for free. But your serial number is generated before that and because this version 3.0 is a paid upgrade you will have to purchase an upgrade.
So you can continue to use version 2.5.9 with your current serial number:
You should not have problem to register version 2.59 with your serial number.
Another option is to purchase an upgrade license.
Thank you!
Best regards,
Revo Uninstaller Support Team