Bug when combining multiple voices/lyrics

[Ruud van Silfhout]

Hi,

Currently my daughter is learning and using Lilypond and she gets a hang
of it. She was busy creating a score of a piec of Mendelssohn "St. Paul's".
She uses the midi files produced by lilypond to practice. 
She got stuck with the attached piece. It simply crashes with:

    Backtrace:
    In unknown file:
       ?: 0* [System_start_delimiter::after_line_breaking #<Grob SystemStartBar
>]
       ?: 1* [Align_interface::alignment_callback #<Grob VerticalAxisGroup
> 1]
       ?: 2* [Axis_group_interface::group_extent_callback #<Grob 
VerticalAxisGroup
> 1]
       ?: 3* [Grob::molecule_extent #<Grob Spanner > 1]
       ?: 4* [Tie::brew_molecule #<Grob Spanner >]

    ERROR: In procedure gh_scm2double:
    ERROR: Wrong type argument: ()
    lilypond: warning: `usr' failed (status 2) (ignored)
               

When processing the voices separately, no problems were encoutered. Just
when the four voices/lyrics were combined, the problem arose. I tried to
strip the piece as much as possible, but it still a considerable amount of
score. The attached zip file also contains the full logfile from which the
previous part was extracted.

Bye,
Ruud

Could you please look into it?

Deel2.zip
Description: Zip compressed data