I'm sorry, but it's just not possible that if you reinstalled after my reply, you would get again that error.
We had a wrong version of the Couatl.exe file online on one of the two mirrors that we use for the online part of the installer, a couple of days ago, but it was online just a few hours, and it has been fixed since then, so if you reinstalled after my reply, it's not possible you would have gotten the wrong version again, because it's not online anywhere now.
As I've said, Reisntall GSX now, and the error will go away, because you'll get the correct version of the Couatl.exe file. You can verify it's the correct version, by checking file properties for the FSX\fsdreamteam\Couatl.exe file. It must be 2.0.0.2364. If it's lower or higher than that, you got the wrong file, so you must reinstall GSX.
About activation, it's totally unrelated to the uninstall/reinstall process. You can uninstall/reinstall GSX an unlimited number of times, but no activation will ever be consumed. You can even uninstall/reinstall the whole FSX from scratch, it won't require a reactivation for GSX too.
The ONLY time you'll have to reactivate GSX, is when you change hardware components, or reinstall Windows from scratch. And even in this case, if you use the "Deactivate" function of the Addon Manager menu before upgrading your system or switching to a completely new PC, you won't consume an activation either.