Case C-526/04: Judgment of the Court (Second Chamber) of 7 September 2006 (reference for a preliminary ruling from the Cour de cassation — France) — Laboratoires Boiron SA v Union de recouvrement des cotisations de sécurité sociale et d'allocations familiales (Urssaf) de Lyon, assuming the rights and obligations of the Agence centrale des organismes de sécurité sociale (ACOSS), (State aid — Articles 87 and 88(3) CE — Tax on direct sales of medicines — Applicable to pharmaceutical laboratories rather than wholesale distributors — Prohibition on implementing a non-notified aid measure — Possibility of pleading that an aid measure is unlawful in order to obtain reimbursement of a charge — Compensation for discharging public service obligations imposed on wholesale distributors — Burden of proof in relation to overcompensation — Detailed rules laid down by national law — Prohibition on making reimbursement of a charge practically impossible or excessively difficult)