I'm gettin the same error.
edit: I got Isabelle to work. Since the npc control file in the game folder had a # in front of the isa_rel bit it never got added to wherever it needed to go I guess. jay_rel also has a # so maybe that'd work for them too.
This only works if ya start a new game. I suppose ya cou save edit the stuff in but that seems like a hassle.
edit2: It did not work for Jay so I jus went back to the event where we meet Jay an made it give me jay_rel either way. I have no idea what I'm doin but it's workin an I feel like I'm choppin up someone else's stuff. Someone please help me.