This same thing hapenned to me. It was a pile of trash on the ground and I was able to fix it by placing another pile of garbage over it, and then taking it out.
Oh and I forgot to mention that I found where the trash was because I couldn't delete the tile it was over, not even with moveobjects on. I was able to delete it by placing the dishwasher on top of it, and then I deleted the entire room and remade it again. I didn't work. When I finished redecorating, the trash was still there.
I hope I could help you :D
