Anyone noticing that you can't get achievements with the trainers on? Is that a new trend or something?
Steams "unofficial" policy is that of not caring what you do to your single-player game as long as you don't affect any leaderboards. The topic of trainers has come up a couple times and the general consensus is that they have better things to worry about.
What game are you having issues with? Maybe someone else has it and can tell you if they got achievements.
I have recently unlocked achievements in Test Drive Unlimited 2, Red Faction Armageddon, and Fallout New Vegas, all with trainers running.
Look at your profile and check if Steam is accurately tracking the game. DG is one of those games that puts you on the leaderboard without your permission. I'll bet you a dollar that it's trying to block your score (because of the trainer), and the result is you getting cut off completely from Steam. That would follow their "don't screw-up the leaderboard" stance and would explain why your achievements are not registering.
All times are (GMT -08:00) Pacific Time (US & Canada). Current time is 6:02:54 AM