ACE related issues belong in the ACE topic, so unless this problem persists in the vanilla game (no mods and/or addons active what so ever) you should post here:
If you are using ACE for OA/CO:
http://www.armaholic.com/forums.php?m=posts&q=11141&n=last#bottom
If you are using ACE for A2 standalone:
http://www.armaholic.com/forums.php?m=posts&q=8943&d=0