This was a dispute concerning whether Community law could prevent the operation of res judicata (under Italian law). ECJ ruled that it could and did in this case.
ECJ: “In the absence of Community legislation in this area, the rules implementing the principle of res judicata are a matter for the national legal order, in accordance with the principle of the procedural autonomy of the Member States”, subject to equivalence and effectiveness principles. Lucchini didn’t change this. The res judicata rule was a procedural domestic rule that governed remedies in a national context for breach of community law. In this specific case it went against effectiveness because of tax considerations etc. However it is not the general rule that res judicata doesn’t apply re community law (as some might interpret Lucchini as saying)