I think I made a mistake because I chose not to ever load the add on manager again.
To have FSX asking again the trust question, do the following:
- Uninstall and reply YES to the question "Do you want to remove the Addon Manager ?" and YES to the question "Do you want to remove the Couatl script engine ?"
- Go to the Control Panel, under "Internet Options", look for the "Content" tab, there should be a "Publishers" button, that will list the software publishers that you trusted, and another tab with untrusted publishers. If you see "Virtuali s.a.s", remove it from both tabs (especially if it's under untrusted)
- Reinstall