simple scenario: 2 staves, 2 lyrics

[Tobias Ulbricht]

Hello list.

I hope to find some answers here. 
I don't understand, how to set 2 voice contexts with a lyrics context for each, 
without encountering some difficulties at some stage.
Consider shortly the following file,

---seymour.ly----------------------

\paper {
    #(set-paper-size "a4")
    indent = 0 \mm
    linewidth = 160 \mm
}

melody = \notes \relative c''
{
    \time 4/4
    \key a \major
    r2
    \partial 2 \times 2/3 {cis4 b4 a4} 
    a2 fis2 ~ fis4. fis8
    \times 2/3 {fis4 gis4 a4}
    e4.(a8) a2 ~ a4. r8
    r2
    r4. fis8 \times 2/3 {fis4 f4 fis4}
    \times 2/3 { a4 (gis4 fis4) } fis2 
    ~  fis4. fis8 \times 2/3 {f4 g4 a4}
    \times 2/3 { c4 (b4 a4) } a2 
    cis2 a2
    r2
    
}

ndvoice = \notes \relative c
{
    \clef bass
    \time 4/4
    \key a \major
    r1
    r1
    r4. fis8 \times 2/3 {fis4 gis4 a4}
    e4.(a8) a2 
    ~ a4. r8 fis8 \times 2/3 {fis4 gis4 a4}
    cis4. (b8) b2 
    ~ b4. fis8 \times 2/3 {fis4 gis4 a4}
    c4. (b8) a2 
    ~ a4. a8 \times 2/3 {a4 b4 a4}
    e'2 e2
}

sopranolyrics = \lyrics {
    Learn how to 
    be more the 
    girl that's in -- side __ me
    with sweet un -- der -- stan __ ding
    with sweet un -- der -- stan -- ding
    stan __ ding
    Sey mours your __ man __
}

tenorlyrics = \lyrics {
    the 
    girl that's in -- side __ you
    with sweet un -- der -- stan __ ding
    with sweet un -- der -- stan __ ding
    with sweet un -- der -- stan -- ding
    Sey mours your __ man __
}

\score {
    \new StaffGroup <<
        \context Voice  = "soprano" { \melody }
        \lyricsto "soprano" \new Lyrics { \sopranolyrics }
        \context Voice = "tenor" { \ndvoice }
        \lyricsto "tenor" \new Lyrics { \tenorlyrics }
    >>
    \paper { }
    \midi  { \tempo 4=100 }
}

---------------------

Then executing "lilypond seymour.ly", or using emacs mode C-c C-d or something.
Using lilypond 2.2.6 debian-sid package.

I worked fine, until I want to start a new line, lilypond finds no break, 
whatever I do.

---
Calculating line breaks... [3]
warning: Could not find line breaking that satisfies constraints.
---

I tried lilypond 2.4.1 debian-sid package, but apart from the changed syntax, I 
get an error:
---
ERROR: Unable to find file "lily.scm" in load path
---

Sorry for the rather big email.
Hope anyone can help me or point me to the right way of doing it or using the 
right version here, or whatever, I'd be glad to here something.

thanks, tobias.