Okay. A Final option that might get this working for you.

Check-in to Your Profile > Select Weapon for FSX > Extended Download Service > Get New Links. Click on that link and download and install it again. You could have an incomplete download. It sounds weird, but it does happen and it has actually happened to me and this final method was the only way to fix the problem that I had.

I hope this will get you going with this great add-on.

Mark