Sounds like maybe he is working with a larger (looser) file tolerance than you… Otherwise I don’t really see a reason why surfaces that were made in V4 that were joinable there would not be joinable in V6…
Hello - one thing I see is that there are many duplicated surfaces in this file… use Explode then SelDup and Delete, then try… It looks like there are many objects that are near-dups, but not quite, so it may take some digging around to find the repeated faces.