and it seems that everybody including the developer is clueless, that's making me afraid.
That's because, if the problem was a bad download, it cannot happen the same to everybody in the same way. Whenever someone report something like this, before replying, I do what the user said it did, so I installed the Stand-Alone Addon Manager again, launched P3D, and it works normally...
Would you like to try a Teamviewer session, so I can check your system directly ? PM if it's ok for you.