The current update works perfectly both in 4.1 and 4.2. It surely won't work in 4.0, because it requires the 4.1 SDK.
So, if you are sure you have P3D 4.1 installed, the only possible reasons why GSX is not working with the current version of the update, are the ones which has been discussed so many times, and are:
1) Faulty antivirus, mistakenly blocking the software because of a false positive bug. This is usually solved by excluding the whole Addon Manager folder from the antivirus scanning, and run the FSDT Live Update again
2) Missing/Corrupted VC++ libraries in your system. See solution in the "Addon Manager not showing up in P3Dv4 **SOLVED**" thread:
http://www.fsdreamteam.com/forum/index.php/topic,17484.msg122656.html#msg122656