Just to make it all the more difficult, the version of GFWL that the game installs is sometimes buggy. What you have to do is uninstall GFWL, manually dl and install it from Microsoft, then install the game, dl the update it asks you about, install it in your Ace Combat folder in SteamApps, and then relaunch it so you can download your profile.
THEN you can go about switching to the Steamworks version that beatyas mentioned.
I downloaded the new trainer that was updated for this game, but it does not seem to work. I am using the latest Steam version of the game, but I am still using GFWL - I have not installed anything to remove GFWL (though I hear that it will be mandatory in April).
The trainer finds the game, I get the Trainer Activated sound when pressing F1, but when I play the game, none of the trainer options work.
NOTE: before this latest trainer from 26-Feb-2014, the game would crash when I had the trainer activiated, so this makes me pretty sure I am using the latest version of the trainer.
Also noteworthy, I installed the last official GFWL update before I switched to the "acah-2.0" Opt-in. ( this was to allow the saves from the MS-GFWL version to be retained in "acah-2.0 NO G4WL" )
If anyone has gotten the trainer working, please share the steps that worked with the rest of us, please.
-Thanks for keeping up with this, 0x90.
( EDIT ) I fiddled with the trainer a bit, and it works for me now. It doesn't respond as quickly as before, and sometimes fails to register my keypad inputs completely. I am sure this is not the trainer's fault however.