Poser stores the runtime libraries info in: RuntimeprefsLibraryPrefs.xml On a couple of occasions when I was guilty of (foolishly) moving and re-naming runtime libraries outside of Poser 5, I had to delete the file because Poser had problems subsequently re-starting. Deleting the file allows Poser to re-create another one (with just the Download library present). You will of course need to point P5 to your library locations again, but at least you'll be up and running. (backup the old LibraryPrefs.xml first JIC of any - unlikely - problems)