I got a PM from one nice guy at RealFlight with some more things to try and those failed as well. I have not heard back from them on my last message begging for a workaround that would allow me to perform the Add-On3 installation without an attempt to upgrade G2 (which as I agree with you, is the cause of the MS error we get). I'll keep pinging them in the hopes that they will eventually help me.
ORIGINAL: plane_pilot
It looks like I have the same problem. I finally upgraded G2 after many attempts. Now I have tried to install vol 3 with no luck. I went straight to the setup.exe and I get the same error to report to MS. Like the previous post, I am in SW development. I have no other problems with applications on my PC except for this one disk. I have yet contacted support to let them see for themselves the problem. Maybe they will trade me for another volume???