Subprocedimiento problema problema

Me gustaría mostrar una lista de valores delimitada por comas en un List . Desafortunadamente, recibo un error que lee Microsoft Outlook got an error: Can’t continue joinList. cuando intento usar el sub-procedimiento que realiza la unión:

tell application "Microsoft Outlook"
  ...
  set addressList to {}
  repeat with theAddress in the theAddresses
    if addressList does not contain (address of theAddress) then
      set addressList to addressList & (address of theAddress)
    end if
  end repeat

  display dialog joinList(addressList, ";") <-- error here
  ...
end tell

on joinList(aList, delimiter)
    set retVal to ""
    set prevDelimiter to AppleScript's text item delimiters
    set AppleScript's text item delimiters to delimiter
    set retVal to aList as string
    set AppleScript's text item delimiters to prevDelimiter
    return retVal
end joinList

¿Qué estoy haciendo mal?