In order to stop Norton antivirus from automatically blocking Free VPN by Jailbreak VPN, you need to disable its Auto-Protect feature. To do this, double click the Norton icon from your system tray (in the lower-left corner of your screen, close to where the clock is), go to Status, then click the Auto-Protect option and press the Turn Off button.
Now you can download and use the software that was blocked, but don't forget to repeat the process and turn the protection back on once you're done.