HI armaholic!! I´m from Argentina, so first forgive my awful English.
I where having troubles with default ArmA missions as well as many players including from this site. I´m refering to chopper involving missions like the pilot training mission or "The grate battle". The bug makes the mission to fail after trying to start engine.
So I tried the older version of ACE (1.07) and the bug wasn´t there. But, using this version you miss all other fixes like performance enhancement or parachute fix. Then discovered that the problem was only the addon file "ace_sys_engine.pbo", so replacen the new one wiht the 1.07 version file solve the problem and you can play those mission using ACE.
I want to share this with you.
Also uploaded this file so you dont have to download ACE version 1.07!!!!
Paste the file on your @ACE/Addons folder. Make backup first!!!!
ACE mod - Engine start FIX