Tangled up in Lilypond syntax

[Tim Slattery]

I'm setting a fairly short song. It's sixteen measures, in the
standard four voice parts. I used Frescobaldi to set up the basic
structure, so the syntax I'm using comes from modifying what it put
out.

What causes the grief is that the last measure in the soprano part is
polyphonic (or polyrythmic). That necessitated a second soprano voice,
which skips the first 15 measures and has three notes in the last
measure.

Lower down, Frescobaldi generates this language:

sopranoVoicePart = \new Staff \with {
  instrumentName = "Soprano"
  midiInstrument = "choir aahs"
}  {  \sopranoVoice }
\addlyrics { \verseOne }
\addlyrics { \verseTwo }

Since I now had two soprano voices, I did:

sopranoVoicePart = \new Staff \with {
  instrumentName = "Soprano"
  midiInstrument = "choir aahs"
}  { <<  \sopranoVoice \sopranoVoiceTwo >> }
\addlyrics { \verseOne }
\addlyrics { \verseTwo }

which results in several error messages like this:
programing error: No spring between column 0 and next one

Makes no sense to me. It does create a PDF, but its all jumbled with
titles, staffs and notes printed on top of each other. And no words
for the soprano part at all.

I'm not an expert in Lilypond syntax, so I'm at a standstill. What do
I need to do to make this work?

Thanks

-- 
Tim Slattery
tim <at> risingdove <dot> com