i was here initially for the low ball nut jokes ...but the problem is a bit like neck curvature, you need to be able to pull the string down on the first fret fretted at the second but only just like a razors width, if it's not doing that then you might need a new nut or at least something under the string at the nut to raise it a tad. Of course nuts can wear, every time you tune up it's gets worn albeit very slightly.