JUDGMENT OF THE COURT (Second Chamber) of 15 January 1998 in Case C-125/96 (reference for a preliminary ruling from the Hessisches Finanzgericht, Kassel): Hartmut Simon v. Hauptzollamt Frankfurt am Main (Additional milk levy - Date on which it becomes payable - Article 15(4) of Regulation (EEC) No 1546/88 - Meaning of 'any levy amount due')