midi set instrument problem

[Thomas Spuhler]

Lilypond doesn't like my midi section:

  \midi { 
        \context {
                \Score
                tempoWholesPerMinute = #(ly:make-moment 90 4)
                }
                \set Staff.midiInstrument =  "recorder"
        }


 I get:
score.ly:20:16: error: syntax error, unexpected \set

                \set Staff.midiInstrument =  "recorder"

I actually took it from a sample and changed the instrument. recorder is in 
the list of the manual.
When deleting the  \set Staff.midiInstrument =  "recorder" line, it compiles.

-- 
Thomas