I faced this myself in my last challenge. First, you have to be sure all broken things have either been replaced or deleted. I chose replace since the challenge does not allow for cheats. This means check your doors, windows and even your lamp posts to see if they have a replace option. Now, here is a tricky one. I had a garden that was wasted but it does not look wasted. You only knew it was wasted because you could do nothing with it even though your garden keeps growing and gets weeds. I had to go in to buy mode and delete them.
After this, I did have to do a slight cheat as the notes I read upon this problem recommended this to get the stuck mail box and garbage can fixed.
Cheats console open (control plus alt plus delete in case you have not used this option before)
testingcheatsenabled true <return>
shift+click brings up object as an option
Click on object and it gives you the option to delete.
Save your game after deleting both your trashcan and mailbox.
Reboot your whole game and reload. Your mailbox and trashcan should be back in place and fully functional.
When I tried this I made sure to do it in a second copy of my game just to be on the safe side. One can never be too careful.
I wish you much luck and hope this works as well for you as it did for me.
I know some of the directions here are listed in other parts of the forums. I merely added them here to save anyone who is searching for the answer the trouble of looking in more then one area.
Could you please confirm if this worked for you for the benefit of others who might also face the same challenge?
Many Thanks. :-)