Can't make changes to build

I have a problem/bug in Build Mode, and it is not the same as what is described in this first post of this thread, but because it's a Build Mode bug and it's also relevant to the topic of this thread, I thought that I should post it here.

First (as I'm not sure if this is a relevant info), I mention that the build that I was trying to build was a Shell build that I had downloaded from the Gallery (it was an empty Shell - it was for a Shell Challenge). I had placed it on a 30x20 lot in Evergreen Harbor.  I had a sim on the lot when I placed the build to the lot. I started to build and everything was normal. Later (next day) I had moved the sim off from that lot (in Manage Worlds) and I went to the lot and I wanted to continue building the house. But then, I couldn't do anything: I tried to extend one room inside the house (make the room bigger) but it didn't work and there was a 'note' appearing which said something like this: "cannot edit an area which is not owned". That is very weird, because it was a normal residential lot (and it had been since I started building). I don't have the For Rent -pack, and I don't have the new Businesses And Hobbies -pack either. I tried to do other things: changing the roof, or moving a door etc. but nothing worked and that same weird note occured every time I tried to do anything. I couldn't continue building. Then I tried to bulldoze the lot (thinking that maybe it would reset the lot and the bug would go away, and maybe I could then continue building), but then the game got stuck in "loading" (there was that "rolling blumbobs circle") and it didn't proceed anywhere, so I had to quit the game via Task Manager.

After that I tried couple more times to go again to the same lot to try continue building but the exact same thing happened. Building was impossible. And there was that same weird note occurring each time I tried to do anything ("cannot edit an area which is not owned"). I wonder how and why this is happening, when it is a normal residential lot and I don't have the For Rent & Businesses And Hobbies -packs. There seems to be some kind of weird bug affecting Build Mode because of the new pack, even when not having the new pack. 

I don't use any CC or mods. I play on Windows (10) PC.

Does anyone else here have similar problem?