an already unpacked one I downloaded from the page of the server I'm using
You used the same download previously? Have you perhaps tried a different download? I'm not an expert on downloading it, since I still have my install CDs, but I had a buddy who was having issues after downloading it, and he tried a different torrent and it worked after that. Perhaps there is something wrong with the wc3 you downloaded. If there was, it could explain how, when you started up a new map with reg WE, it wouldn't work.