Hi Pete,
I haven't written to you before, but I just want you to know that I have had a problem running FSUIPC and the anti-virus and firewall package McAfee in FSX. After reading through a number of posts here, I decided to uninstall McAfee's Privacy Service to see what would happen. And you wouldn't believe the results. Once I uninstalled the Privacy Service, I immediately saw the add-on menu in FSX and the FSUIPC tab!
I have been in contact with McAfee about this. Their anti-virus and firewall package is top-notch, but I'm afraid it imposes restrictions of some sort on FSX and weather programs such as Active Sky. Certainly hope they can do something about this. Please note that this issue is only related to their Privacy Service - and not the anti-virus and firewall.