strange error after reducing music rhythm by an half

[Federico Bruni]

Hi

while transcribing a piece of music, I realized that it may work better 
if written with a different rhythm, so I used the Frescobaldi option 
which reduces the rhythms by an half. Then I removed all the bar checks.

But I cannot compile this modified file and I don't have a clue of the 
reason why. Below you find the verbose output and the error message. Is 
it enough to figure out what the error can be?

It's copyright music so I cannot post it here. If someone wants to see 
the file I'll send it privately.

Thanks in advance,
Federico

%% Output

Interpreting music...
[/home/fede/lilypond-git/out/share/lilypond/current/fonts/otf/emmentaler-20.otf]/home/fede/lilypond-git/out/share/lilypond/current/scm/lily.scmBacktrace:
In /home/fede/lilypond-git/out/share/lilypond/current/ly/init.ly:
  61: 11* (let* ((book-handler #)) (cond (# #) (# #)))
  64: 12  (cond (# #) (# #))
In /home/fede/lilypond-git/out/share/lilypond/current/scm/lily-library.scm:
    ...
 213: 13  [ly:book-process #<Book> #< Output_def> #< Output_def> 
"HalfwayHome"]
In unknown file:
   ?: 14* [determine-frets #<Context TabVoice=tab first voice () > (#) 
(# #)]
   ?: 15* (letrec (# # # # ...) (let* # #))
In 
/home/fede/lilypond-git/out/share/lilypond/current/scm/translation-functions.scm:
 511: 16  (let* (# # # # ...) (if # # #))
    ...
 540: 17  (let* ((string-frets #)) (if (null? grob) string-frets ...))
 541: 18* [determine-frets-and-strings (#) (8) (()) ...]
In unknown file:
   ?: 19  (letrec (# # # # ...) (let* # # # ...))
In 
/home/fede/lilypond-git/out/share/lilypond/current/scm/translation-functions.scm:
 397: 20  (let* (# #) (for-each # pitch-alist ...) ...)
 401: 21* [for-each #<procedure #f (pitch-entry string-fret-finger)> 
((# . 0)) ...]
In unknown file:
   ?: 22* [#<procedure #f (pitch-entry string-fret-finger)> (#<Pitch g 
> . 0) (8 #f)]
In 
/home/fede/lilypond-git/out/share/lilypond/current/scm/translation-functions.scm:
 403: 23* (let* ((string #) (finger #) (pitch #) (digit #)) (if (or # 
#) (if # # #)))
 411: 24  (if (or (not #) (eq? digit 0)) (if (eq? digit 0) (let # #) 
(let # #)))
    ...
 424: 25  (let ((this-fret #) (handle-negative #)) (cond (# #) (# #) (# 
#)))
 425: 26* [calc-fret #<Pitch g > 8 ...]
 313: 27  [* 2 ...
 313: 28* [- -5/2 ...
 313: 29* [ly:pitch-tones ...
 313: 30* [list-ref (#<Pitch e' > #<Pitch b > #<Pitch g > ...) {7}]

translation-functions.scm: In procedure list-ref in expression (list-ref 
tuning (1- string)):
translation-functions.scm: Argument 2 out of range: 7