No string for pitch #<Pitch

[Jesús Guillermo Andrade]

Currently, I am trying to set up a complete implementation of the  
venezuelan cuatro into lilypond.
So far, I've been able list most chord shapes, but I keep getting  
errors in the form of:

advertencia: No string for pitch #<Pitch gis' > (given frets ())
advertencia: No string for pitch #<Pitch e' > (given frets ())
advertencia: No string for pitch #<Pitch a' > (given frets ())
advertencia: No string for pitch #<Pitch ges' > (given frets ())

What does these mean? I have read many of the .scm source files and I  
still cannot understand.

Any ideas?


Guillermo