I had to first remove the older version of SODE as when I try to install latest version of GSX it installs SODE and wont allow me to register it. A error prompt Category=add-on package, operation=add,title=sode,path=C:\program files x(86)12bpilot\sode\p3dv3 file argument is mandatory.
The problem doesn't have anything to do with GSX. It's a message from SODE, and it's caused by the fact your Prepar3D is outdated, you are probably using 3.2 or below, because SODE is trying to use a feature that has been added in 3.3 only, which is to call Prepar3d.exe from the command line, to configure an addon, which is an easy way to "register" an addon, without having to deal with the configuration files themselves, because the sim offer this service already.
The GSX installer checks that and, if you are on 3.2 or below, it doesn't use that method but, apparently, SODE must have assumed that, if you use P3D 3, you should at least have 3.3.
I strongly suggest to update P3D to the latest 3.4 Hotfix.