Midi command not working with Mac (OS X 10.5.2)

[Io D .]

When using the lilypond program on my
 Mac computer, adding a \midi block 
does not result in a midi 
file being produced.  Is this a known 
bug or more likely a problem in my own coding?

CODE:

upper = {
\clef treble
\tempo 8 = 240
\override Staff.TimeSignature #'style = #'()
\time 2/2
\key c \major

<f' bes'>4 \times 2/3 {<f' bes'>8 
<f' bes'>8 <f' bes'>8} <f' bes'>4 r4
r4 \times 2/3 {<f' bes'>8 <f' bes'>8
 <f' bes'>8} \times 2/3 {<f' bes'>4
 <f' bes'>4 <f' bes'>4}
<f' bes'>4 \times 2/3 {<f' bes'>8 <f' bes'>8
 <f' bes'>8} <f' bes'>4 r4
\break
r4 \times 2/3 {<f' bes'>8 <f' bes'>8 <f' bes'>8} 
\times 2/3 {<f' bes'>4 <f' bes'>4 <f' bes'>4}


}


lower = {
\clef bass
\override Staff.TimeSignature #'style = #'()
\time 2/2
\key c \major
<ees' bes>4 r4 <des' aes>4 r4
<ees' bes>4 r4 <des' aes>4 r4
<ees' bes>4 r4 <des' aes>4 r4
\break
<ees' bes>4 r4 <des' aes>4 r4
}
\score {
        \header {
                title = "Rainy Wednesday Theme"
                composer = "Io Daly"
        }
        \new PianoStaff <<
                \set PianoStaff.instrumentName = "Piano"
                \new Staff = "upper" \upper
                \new Staff = "lower" \lower
        \midi { }
        
        >>
}

\paper  {
                                %#(set-global-staff-size (* 5.8 mm))
  interscoreline = 2.\mm
  between-system-space = 15\mm
  ragged-bottom = ##t 
}



\version "2.10.33"