song with multi-voice ending

[fiëé visuëlle]

I've a song with one voice, but the ending has three.
I need those in different staves, because they've slightly different  
texts, but I didn't manage it yet.
What's wrong with my code below?

The first (one voice) part works.
---
\score {
        {
                <<
                        \context ChordNames {
                                \germanChords
                                \set chordChanges = ##t
                                \akkorde
                        }
                        \context Staff = Oben <<
                                \global
                                \context Voice = "eins" { \hauptstimme }
                        >>
                        \lyricsto "eins" \new Lyrics { \text }
                >>
                <<
                        \context ChordNames {
                                \germanChords
                                \set chordChanges = ##t
                                \akkordeSchluss
                        }
                        \context Staff = Oben << \context Voice = "eins" { 
\schlussEins } >>
                        \lyricsto "eins" \new Lyrics { \textSchlussEins }
                        \context Staff = Mitte << \context Voice = "zwei" { 
\schlussZwei } >>
                        \lyricsto "zwei" \new Lyrics { \textSchlussZwei }
                        \context Staff = Unten << \context Voice = "drei" { 
\schlussDrei } >>
                        \lyricsto "drei" \new Lyrics { \textSchlussDrei }
                >>
        }
        \layout {
                indent = 0\cm
        }
}
---
LilyPond says:

Analysieren...
Interpretation der Musik...[8][16]
Vorverarbeitung der grafischen Elemente...
Interpretation der Musik...
Programmierfehler: Moment is not increasing. Aborting interpretation.
Fortsetzung, die Finger kreuzen
[7]

(I don't think the translation of the error messages was such a good  
idea...)




Greetlings from Lake Constance
---
fiëé visuëlle
Henning Hraban Ramm
http://www.fiee.net
http://angerweit.tikon.ch/lieder/
https://www.cacert.org (I'm an assurer)