The reason I asked is because the message you got about not being able to place a lot on a road reminded me of the very much out of place invisible road segment I found in a world from My Sim Realty. I actually had placed a lot on that spot in CAW, but when I play tested, a taxi drove right onto the lot to pick up my sim. I removed it in CAW by clicking where it was, then when the lines for moving a road segment appeared, I was able to delete it. Did you try starting a new game in that world, then placing a sim in the same house and testing to see if you get the same issue? If it is an out of place road segment, you can't remove it in game. It probably isn't, but you never know. It could also be some other world object that is hidden just below the surface. World objects don't show up in an MC search.