Mark, I think that the pre slotted nut is too low. It is meaning that the first fret is becoming the take off point. I have put a piece of card, about a low E string thick, under the nut, and the problem has gone. Did I not sand the fretboard enough, so I learn from this. Is it a reasonable plan to glue a thin bit of wood on at the nut to raise the nut enough, them adjust nut as necessary down to the right take off height? Thanks Geoff