As explained so many times on the forum, you should never "turn-off" the antivirus ( they are never really turned off, unless you uninstall it ), but instead you must:
- Add the WHOLE Addon Manager folder to the antivirus exclusions list.
- Run the FSDT Live Update again
Also, please clarify if you are only missing the GSX menu ( as your subject says ), or you are also missing the Couatl menu ( but still have the Addon Manager ), or if you are missing all menus.