: On some Windows systems, the license key may fail to save if the program isn't run with elevated privileges. Right-click the application and select "Run as Administrator" before entering the key. 3. The Risks of "License Key Lists"

FlashBack Pro 5 stores its primary license list here: Computer\HKEY_CURRENT_USER\Software\Blueberry Software\FlashBack Pro 5\License

Sometimes the license configuration file becomes corrupted. A fresh start often clears the "invalid key" loop. FlashBack Pro 5 via the Control Panel.