How to create a header within a \new score

[Jean-Alexis Montignies]

Hi all!

I'm trying to have a score created with a header within a book (which  
have its own title). It works if i use \score, but as soon as i use  
\new Score, it tells me: unexpected header;

    \new Score \with {
        proportionalNotationDuration = #(ly:make-moment 1 8)
    }
    {
        <<
            \new ChordNames = "chords" {
                      \harmoniesSolo
                }
            \new Voice = "headVoice" {
              \solo
            }
        >>
        \header {
                piece = "chords for solos"
        }
    }

How to do this?

Jean-Alexis Montignies