You Anti Virus software probably deleted it!
Even if you turn off/disable your AV when installing, once you turn it back on, it will eventually "find" it again, and delete it.
Reinstall with your AV off, then once the installation is complete, and before you turn the AV back on, add the ace_757.exe to the AV exclusion list, then turn the AV back on.

ace_757.ex is found in the <FlightSim>\Captain_Sim\757-III\ace folder.

Note. Replace <FlightSim> with Microsoft Flight Simulator X, Prepar3D v3, Prepar3D v4, or FSX (for FSX-SE, in the Steam, or SteamLibrary)