The neck on my Cumberland has something wrong...One day the higher notes (around the octave) on the high E and B strings would not play. And it's literally like, one day it was good...the next it wasn't. On the E string if you fret the high F, F#,and G, they all sound the same. If you look down the neck from the body, it appears to be even with the body as far as the joint, then does a little dip with a slight bow to the nut. Anybody have any experience with this? I've loosened the nut to see if that will help, but after three days no improvement. I love this guitar! Help!