When I get "error" messages like that it usually means that there's something or things interfering with the placement of the stairs.
The only way I know of how to fix it is to:
1. Build the stairs on the outside of the building and then build the house around it.
2. Move the objects/decor and roof out from the space where you want to add the stairs and replace those items/objects/decor and roof and flooring from the ceiling when finished placing the stairs.
-- Make sure you've got level ground to work with, or it may not allow you to place stairs.
I found the house you're talking about and was able to add a spiral staircase behind the bathroom. (added the stairs to outside of house)
Click image to see larger view.
I built a wall around it and added an archway, flooring, wall covering, a light, windows and a door to the room with the two single beds in it, as it didn't originally have a door.