So I downloaded the latest Add-On Manager from your Website, installed it and the result was that during FSX (Acc) startup a couatl error message for every single FSDT airport appears, which mentions that a couatl reinstallation might solve the problem.
This shouldn't simply happen unless, for some reason, you thought you downloaded the current version, but you got an old one, possibly because the browser has changed the file, so you still got the old one.
I didn't find any couatl entry in my Vista Startup-Menu, so how can I reinstall couatl?
Because the message did not say to reinstall Couatl, the message says to reinstall the Stand-alone Addon Manager, which it's just what you did, but it has to be the latest version.
However, the whole point is not relevant in any way to PHNL: the only way this might have happened, is if you installed PHNL, uninstalled it, never reinstalled it, then reinstalled another FSDT scenery.
In THIS case, and this case only, you should use the Stand-alone Addon Manager installer, to restore all the updates that PHNL installer added and apply them to your other FSDT sceneries, without having to have PHNL installed, if for some reason you decided to not to keep it.
Instead, in your case, you should simply had to reinstall PHNL, and that's it.
Not that installing the Stand-alone Addon Manager wouldn't make any difference: the file relevant to it are exactly the SAME as PHNL, just that the Stand-alone Addon Manager doesn't have the scenery.
Provided, of course, the Stand-Alone Addon Manager you have installed IS the last version, which was uploaded together with PHNL.
So, you can either try to fix it by CLEARING YOUR BROWSER CACHE, and re-download the Stand-Alone Addon Manager, in order to be sure it's the latest verison.
You can simply:
- Uninstall PHNL, reply YES to BOTH questions "Do you want to remove the Addon Manager?" and "Do you want to remove the Couatl engine?" and don't worry about any missing file messages. This will clear your system entirely.
- Reinstall PHNL. No need to do anything else afterwards, because PHNL comes with all the lastest files already.
Now, this will surely fix your PHNL installation, but the stuttering issue is an entirely different one, which wasn't fixable of course by unisntalling/reinstalling, becase it's not casued by the scenery for sure, but it should be something else.