Whenever I try to register the serial for GSX it gives me a popup to run FSX in Window mode.
If the Addon Manager says you are not running in Window mode, there might be a problem with your FSX.EXE, possibly is not the correct version or the Addon Manager is forced to run in P3D mode. Have you ever installed P3D in your system ? Have you set the forced detection as explained in this thread ?
http://www.fsdreamteam.com/forum/index.php/topic,7237.0.htmlIf you set that variable NOT as explained in that thread (using a batch file that sets and the un-sets the variable when exiting), but in another way, for example by setting an environment variable that stays set, this will cause this problem.
As a matter of fact, I am already in Window mode based on my research I have seen many people facing similar issues with either GSX or any other scenary associated with the Addon Manager.
Nobody ever had this problem with FSX only. Some are having it when using it together with P3D if they use the Migration tool, which will conceal P3D to act as FSX, but it will be fixed by disabling during the activation, and if they set the variable explained in the above thread in a different way that what is explained in that thread.
Please, confirm if this is the case.