What add-on manager version are you running? I have 4.0.0.3 and I am getting the QW757-2 error, on both P3D and FSX.
The one and only version that come with and works with KCLT (that's why I show KCLT), which is the same everybody would get by installing KCLT or any other FSDT installer, and since it gets downloaded automatically online, it's very difficult to get the wrong version by mistake.
Since my two screenshot clearly prove there are no problems between the QW757 and the new Addon Manager, here's a possible list of things to check:
- Installing the QW757 after any FSDT product using the new installer will cause problems, because it will "downgrade" the Addon Manager, since we still don't have an update QW757 installer that comes with the new Addon Manager AND downloads from the new server.
That's why we always say to install the Stand-Alone Addon Manager as last.
- The antivirus might have blocked just Couatl, which is required by the new Addon Manager, this might be the case if the code displayed is QW757-2
- If you have the QW757-4 code, instead, it means the Addon Manager is just not running but, in this case, nothing will run, no KCLT, no GSX, nothing. In this case, the usual suggestions applies, disable the antivirus while installing, configure the antivirus to exclude the Addon Manager folder.
If the antivirus is not the problem, it might be a problem of missing VC++ runtime libraries. The new Addon Manager requires both the 2013 and the 2015 version to be installed. Of course, it comes with them, and installs them, launching the official installer from Microsoft but, if you have a *problem* with them, the installer won't fix it.
Sometimes, it might be enough to reinstall the Addon Manager and restart Windows, to complete a pending installation of the VC++ libraries.
But again, I can only repeat and confirm, there are no problems whatsoever between the QW757 and the new Addon Manager, as seen in the screenshots from P3D and FSX:SE.