Umberto's suggestions by installing the newest AM, the newest FSDT sceneries as well as the newest QW B757 from scratch and then all worked fine.
If you did *exactly* like that, it's no wonder nothing is working, because you did it on the opposite order. In all my suggestions, I always stressed the most important thing is, whenever the QW 757 is involved, that it must be installed BEFORE other recent products.
The reason for this is due to QW never updated their installer to match our latest self-updating installers so, it's "downgrading" the Addon Manager files.
- Uninstall everything, both FSDT and the QW757 and reply YES to the question "Do you want to remove the Stand-Alone Addon Manager ?"
- Reinstall everything
starting with the QW757- Reinstall everything else from FSDT, using only the most recent installers, in any order you like.