Also Couatl Power Products and Addon manager show up in the Add-ons in FSX this issue happens with all FSDT sceneries just fyi.
If you see both menus, this means your issue doesn't have anything to do with anything discussed on the forum (like antivirus, trusting, etc) because, if you see both menus, it means the programs are running correctly.
First, be sure you are using the current version of the sceneries. If not sure, download the current installer.
Also, check if you have the following file:
If yes, post its content.