I traced our authentication server's log and I can see where the installer failed. When you enter your email and license key, the installer "shakes hands" with our server to validate your entry. There is a slight hesitation during that validation but when complete, the installer prompts you for more information. In your case, that validation process never completed and it left your license key locked. I don't think you did anything wrong and our server doesn't show an error. I'm pretty sure this is not related to your antivirus, so please re-enable it. It might be an unlucky case of an Internet hiccup.
Can you send me all of the files in your %TEMP% folder that start with bitrock_ ? These might shed some light into why the process didn't complete. The %TEMP% folder is something like this: C:\Users\<USERNAME>\AppData\Local\Temp, where <USERNAME> is your user-id on your computer.
I unlocked your license key on our server. You can run the installer again without the "license key was already used" error. After you enter your email and key and click next, have a little patience. Maybe the process is a little slower on your system.