Hi –
I dont exactly know the answer but I have had weird problems before which I managed to get round by doing the same thing by a slightly different route …..
……what I am thinking here is loading the project file / import assets individually into the project / then insert assets into layers by holding down the alt key and dragging …
OR — maybe adding required assets to a new layer / copying settings over / then deleting old layer …..
…………………. just a thought ——- chris —