You sleep-darted a certain someone and lost the clean hands achievement?

I beat the game, got flesh/steel and ghost- didn't get clean hands- heard about the glitch with the sleep dart against You Know Who. Redid said mission without sleepdarting, just pickpocketed required item and bolted- beat the mission, no kills, still no achievement...

Ugh...

Maybe you hit him in the head with a sleep dart.
I'm not positive but I think that might kill them.

The person the OP is talking about...isn't a him. I never went for Clean Hands yet, so I can't really answer the original question. Maybe you should post this in the spoilers section, so you can talk about it in more direct terms?

They 'die' no matter what. Can't do it.

Sebor13- You misunderstood

Rhonos- I didn't even engage either of them? What do you mean they die no matter? I don't sleep dart or choke out. Neither, but they still count as dying?

New to the forum, will find spoiler section, thanks guys

You should just be able to restart the mission. I pickpocketed the key with time stop and I ended up getting Clean Hands and Ghost for that playthrough. Unless it is a glitch, there is probably some other occasion that someone was accidentally killed. I restarted it from a hard save not from the menu, I don't know if that makes a difference.