Did you try to decrap the files even though they are not store content?
I can't remember if I have had a non-store item say that. I am sorry I am not much help. I would try decrapping if you haven't.
I think I've solved the problem, sort of. I actually did decrap the world before installing it, and I did it again when I redownloaded it in case it had gotten corrupted or something. This time I tried again with the non-decrapped version, and that worked. The description of the world says the only EA content is a couple of paintings, so it's no huge loss, but I wonder why that happened? I was just decrapping everything in case some of it contained store content. Are we not supposed to do that?
I'm going to try it with the rest of the files and see if the same thing happens.
[ETA: Yep. At least with the houses I decrapified, it seems to have solved the problem to install the non-decrapped versions. I haven't tried it on a few doors and plants I got from TSR because I decided I don't need them enough to redownload them anyway, although I wonder why I would have decrapped them in the first place.]