Well, it is possible for those who have "electronic copy" of the disc or the real one, and because of that even after upgrading installation to full some files weren't copied to the game folder.
Not sure but I think that d2xmusic and maybe d2xvideo .mpq are the files that needed to be manually copied to the game folder iirc so the user doesn't need to have expansion disc inserted.....
But is that the problem or not is another thing.