Hello,
First of all: I have the 767 III from you CS, and no problem for the installation and for ace. :)

I just bought the 757-III for P3Dv5.
Ace_757.exe has disappeared. The downloaded liveries install but are not visible in the available aircraft list??? :-/

I followed your explanations. And tried a complete re-install
1. I'm Make sure my Windows and all drivers are up to date. OK
2. Reboot your computer. OK
3. Turn off your antivirus including default Windows Defender OK
4. Make sure your sim is not running. OK
5. Uninstall the Base Pack. OK
6. Delete all residues/mods of the product from your sim OK
7. Delete all old flights/scenarios from ...\OK
8. Check the product's Sim Ops>Updates page and make sure you are going to install the latest version of the product. OK
9. Double-check you are going to install a proper product version matching your flight simulator version OK.
10. Turn OFF your VPN (if applicable).OK
11. Install the Base Make sure you always run the installer .exe files as administrator. OK
And following all that I have this message;https://imagizer.imageshack.com/img924/787/6FJeLT.png

it's still painful, right?
Can you explain to me, thank you