Unresolvable rest collision?

[Ted Lemon]

I'm getting a puzzling error message when I try to typeset the following 
lilypond source file.   The error is being reported in measure 17 in the first 
bass clef voice (\vba).   The error that's reported is "romanza.ly:143:47: 
warning: cannot resolve rest collision: rest direction not set".   Can anyone 
see what it is that I am doing wrong here?

#(set-global-staff-size 22)
\header{
  title = "Romanza"
  composer = "Wolfgang Amadeus Mozart"
  arranger = "Arr. by M. Moszkowski"
  copyright = "July 1919"
  subtitle = "from Concerto for Piano in D minor"
}

#(set-global-staff-size 21)

keyMeter = { \key bes \major \time 4/4 }

\parallelMusic #'(vta vtb vtc dynD vba vbb vbc) {
  % 1
  f'2-4(\< e8 f e f\! |
  s1 |
  s1-"c espress." |
  s1\p |
  \stemUp d'2_3_5^( cis8 d c d |
  \stemDown bes'4 bes bes bes |
  s1 |

  % 2
  g8\> f ees d d4\!) f8.( d16 |
  s1 |
  s1 |
  s1 |
  ees8 d ces bes) bes4 r |
  bes4 r r2 |
  s1 |

  % 3
  bes8) r bes r f r f r |
  s1 |
  s1 |
  s1 |
  d,8^( f d f ees f ees f |
  bes,2 <c a> |
  s1 |

  % 4
  bes4.^"a)"( c16 d <a c>8-1-2 d ees e-1 |
  s4 s\turn s2 |
  s1 |
  s1 |
  d8 f d f f,4) r |
  bes2 s2 |
  s1 |

  % 5
  \break f2-1)( e8\< f e f\! |
  s1 |
  s1 |
  s1 |
  d''2^( cis8  d cis d |
  bes'4 bes bes bes |
  s1 |

  % 6
  g8\> f e d d4\!) f8.( d16 |
  s1 |
  s1 |
  s1 |
  ees8 d c bes bes4) r |
  bes4 r r2 |
  s1 |

  % 7
  bes8) r bes r f r f-5 r |
  s1 |
  s1 |
  s1 |
  d,8( f d f c f c f |
  bes,2 <a f> |
  s1 |

  % 8
  <f,~ a c ees>2^( <f bes d>8) bes'_[_( c d] |
  s1 |
  s1 |
  s1 |
  bes,4_\finger \markup \tied-lyric #"3~1" f  bes,) r |
  s1 |
  s1 |

  % 9
  \break ees4. \stemUp \tuplet 3/2 { d16 c bes } \stemNeutral a8) c8^[( d ees]
  |  s1 |  s1 |
  s1 |
  s1 | r8 f'8~ <f~ a~>8 <f~ a~ c~ >8 <f a c ees>8 r8 r4 |   s1 |

  % 10
  f4. \tupletNeutral \tuplet 3/2 { ees16 d c } bes8) f'8_[( g a] |  s1 |  s1 |
  s1 |
  s1 | r8 f8~ <f~ bes~>8 <f~ bes~ d~ >8 <f bes d f>8 r8 r4 |   s1 |

  % 11
  bes4. \tuplet 3/2 { a16 g f } e8) g8_[( a bes] |  s1 |  s1 |
  s1 |
  r8 c'8~ <c~ e~>8 <c~ e~ g~ >8 <c e g bes>8 r8 r4 |   s1 |   s1 |

  % 12
  c4. \tuplet 3/2 { bes16 a g } f8) f8_[--( 8-- 8--] |  s1 |  s1 |
  s1 |
  s4. f'4.^( r8 r |
  r8 f8~ <f~ a~>8 <f a c >4 d'8_[ ees c_4 ] |   s1 |
  
  % 13
  f2)( e8_[ f e f] | s1 | s1 |
  s1 |
  d2)^( cis8 d cis d |
  <bes, f' bes>8\arpeggio r bes'4 4 4 | s1 |

  % 14
  g8_[\> f ees d\!] d8)^"b)" d_[(\turn f d] | s1 | s1 |
  s1 |
  ees8 d c bes bes4) r |
  bes4 r r2 | s1 |

  % 15
  bes8) r bes r f r f r |
  s1 |
  s1 |
  s1 |
  d,8^( f d f c f c f |
  <bes, f>2 <a f> |
  s1 |

  % 16
  <f,~ a c ees>2^( <f bes d>8)
  \acciaccatura bes bes'( \acciaccatura c, c' \acciaccatura d, d' |
  s1 |
  s1 |
  s1 |
  bes,4_\finger \markup \tied-lyric #"3~1" f  bes,8) r r4 |
  s1 |
  s1 |

  % 17
  <ees, a c ees>4.\arpeggio \tuplet 3/2 { d16 c bes } a8) (c d ees | s1 | s1 |
  s1 |
  c''8\rest <c a>8^( <c a> <d bes> <c ees>4.) f8\rest |
  f8 f'4._~ f e8\rest | s1 |

}

\score {

  \new PianoStaff <<
    \new Staff = "trebleStaff" {
      \tempo "Andante" 4 = 72
      \keyMeter
      \set midiInstrument = #"piano"
      <<
        \new Voice = "tenor-a" { \relative c' \vta } 
        \new Voice = "tenor-b" { \relative c' \vtb }
        \new Voice = "tenor-c" { \relative c' \vtc } >> }
    \new Dynamics { \dynD }
    \new Staff = "bassStaff" {
      \keyMeter \clef bass
      \set midiInstrument = #"piano"
      <<
        \new Voice = "bass-a" { \relative c \vba }
        \new Voice = "bass-b" { \relative c \vbb }
        \new Voice = "bass-c" { \relative c \vbc } >> } >>
  \layout { } }