Talk about a quick response!!!
Deselecting the selection in the page where I got it from (as per your great 'multiLevelHouseGuide') makes no difference at all.
I might also mention that the number behind the error message is quite different, depending on how many/type of objects are part of the ...

Love the tutorial on this subject. Unfortunately it does not work with furnishings in place - for me at least, even taking smaller parts. The copy as new furniture mostly tells me 'Couldn't copy selection as furniture 101776'. Even if it does not give me this message, then more often than not there ...