I think it means no one at that address with the name you put on the address. When the mailman brought the package to that address whoever was there said no one with that name lived there.

That's one reason.  Others include, but are not limited to: House # wrong, Apt # wrong, part or all of name misspelled/illegible, Street wrong, you get the picture.
Generally speaking, carriers will make an effort to deliver the mail, but prefer to err on the side of caution if they are for some reason unsure if the package is being delivered to the correct person/address.
The theory is that it is preferable to return it to you (with the attendant irritation to you) than risk an erroneous delivery and maybe lose the package and contents altogether.
Sort of the lesser of two evils.
Now, if the [i]regular[/i] carrier is off, and a [i]substitute[/i] carrier is working in his stead, the chances of this happening are increased, as the sub will not know the addresses and people on the route as well as the regular guy.

[url=http://www.euservices.com/uspsmail.html]Here Ya Go[/url] [:)]

How's this-Jones and Smith, Architects-split up their partnership and both file changes of address because they want the mail and are stealing each other's clients-so both Jones and Smith say the mail is theirs so the post office says the heck with it and sends the mail back.

OK so that's BS I just made up, but not bad, eh?

Most likely a divorce.