The license-key format in version 3.x has been changed. So, if you wish to upgrade to version 3.x (or higher) you have to obtain a new license code. Don't worry, you've already paid when you have
registered the Pro edition, and your subscription is valid lifetime, so this upgrade IS FREE.
In order to get your new license, please, contact us through the contact form on our web site.
Be aware that if you upgrade from v1.x/v2.x to version 3.x (or higher) without obtaining a new license code from us, SilverSHielD will revert to Free edition, thus with the limitation of only 1 (one) client connection.