Case C-249/11: Judgment of the Court (Second Chamber) of 4 October 2012 (reference for a preliminary ruling from the Administrativen sad Sofia-grad — Bulgaria) — Hristo Byankov v Glaven sekretar na Ministerstvo na vatreshnite raboti (Right of citizens of the Union and their family members to move and reside freely within the territory of the Member States — Directive 2004/38/EC — Article 27 — Administrative prohibition on leaving the territory on account of failure to pay a debt owed to a private legal person — Principle of legal certainty with regard to administrative acts which have become final — Principles of equivalence and effectiveness)