Adobe InDesign CS5 export to IDML

Hi

I cannot export a file as InDesign Markup format:

tell application “Adobe InDesign CS5”
tell active document
export format “IDML” to ((path to desktop) as string) & “exported.idml”
end tell
end tell

I get this error:

error “Adobe InDesign CS5 got an error: The specified object does not support the desired export format.” number 90934

does anyone know how can I export the document?

Try:

export format InDesign markup...