I've finished the mission by noclipping the keypad door in 1 hour 31 minutes. A reason for the crash of saved games could be too many AI's because I had a crash when I tried to reload a save from the city watch with lots of guards.
Open doors on unlock is set to YES. Thanks for the patch. It works but you have to pull the lever twice. You can't use old savegames with the patch. By the way:
Thanks for another great mission ! That's not nice. The archer started shooting from the roof assisted by another other guard making dog food of Mr. Farrell. Me too but the guards took care of the surprise.