It's not quite clear from your post - you are clicking on Dungarees, say, in the library window and then clicking the double tick button at the bottom of the library list, yes? It may well be that the the RSR file in the folder with the OBJ you tried importing (not the one in the library folder) is corrupted - delete it (with Poser closed) and Poser will rebuild it from the OBJ next time you try to use the figure.