Since the software is no longer officially maintained or sold, websites offering "free license keys" or "key generators" (keygen) for Outpost Firewall are highly likely to contain:
: Use Compatibility Mode (set to Windows 7 or XP) if trying to run it on newer hardware, though success is not guaranteed. User Guide - FTP Directory Listing skachat kliuch outpost firewall
: Completely remove any previous firewall software before installing. Since the software is no longer officially maintained