Otherwise you will lose your controller if you change focus to another window. I would also add you need to install FSUIPC if you have an Saitek H.O.T.A.S controller. I would also that after install all 3 legacy simconnect, I would reinstall the newer one in the lib folder. You do need to install from the older version to the newer one. PRO membership payments go directly back into the website to pay for hosting, bandwidth, and development costs. I did a fresh new install of Win 8.1 and ran into the same problem. Signing-up for PRO gives you super fast, unrestricted speed to the thousands of MSFS, FSX, P3D & X-Plane downloads which include aircraft, scenery, and more - click here to view the library for free or. Yes, I was one of the person who struggle with that issue over the weekend. So that is why I shared it here in case someone falls into the same problem as me in order to troubleshoot the issue.
I tried it out 2 times to see if there are any changes, but I didn't see any changes. After selecting the PMDG aircraft, I did not see an activation window. But today I have reformatted my hard drive, because I wanted a clean install of Windows 8.1. Maybe you have both fsx installed on your machine, or you probably deleted the boxed version and kept the FSX Steam Edition only, which would mean that earlier SimConnect version are present on your machine, I don't know, I am just guessing.