Floor tile needed for object?

Try this, in edit town move your sims to the clipboard by evicting them. Now go back to the lot in build mode, use the walls up button and click the level up as high as it will let you and examine the area above these tiles and look for anything from light fixtures to maybe a wall decor and remove it. Also make sure the roof is not on by going to roofs and clicking off the automatic roofs, and then click the delete all roofs button as well. When that is done, go back to Edit town.

Move you sims back into the lot from the clipboard and if the tiles are still there try deleting them with the jackhammer. Let me know if this works, if not the lot itself may be corrupted and I will let you know what to try next.