Sounds like somethings in the way of where theyre trying to go.. Is there ANYTHING at all in the way? Did you place the stairs using moveobjects on?
When the guy passed out he was probably blocking the stairs. If he died in that spot, maybe his urn is blocking the stairs now?
Alright; I have two solutions for you. First option: Move your sims out of the house and delete the old lot. Move them into a new house, all will be well. Of course you lose the old house that way. Second option: Download JMPescado's hacks "struckobjremover.zip" and "ffsdebugger.zip" and install them into the game. You can get those here. Once in the game they are under the misc. folder. The debugger -- try this one first before stuck object; it might clear everything up. It looks like a box. Save your game then place it on your lot. Have any sim click on it and select force errors -- in world. It will ask for a confirmation; allow it to process. (do not do this with the boolprop testingcheatsenabled set to true...it will cause lots of pop-up boxes) It might take several minutes to process but it effectively resets everything on your lot and gets rid of any errors. The Stuck Object remover is a clear object in buy mode; you'll see the outline of where you're putting it in the game and what it does is "zap" any invisible (and visible) object(s) that is blocking your sim's path. You can try playing with that around where the steps are.
