Unfortunately, I'm not sure if there is any way to fix this, other than leaving and re-joining (assuming it isn't a consistent problem, short of restarting). One person reported this problem if they joined during combat, but it was fixed once their turn came around (though I don't know if that would help your case, and it wouldn't be a very convenient workaround if it did).
Did you try joining a new multiplayer game and then you friend loading a current save?
