AGRICULTURE - COMMON ORGANIZATION OF THE MARKETS - MILK AND MILK PRODUCTS - BUTTER HELD IN PUBLIC STORAGE - SALE AT A REDUCED PRICE TO PROCESSING UNDERTAKINGS - RULES ON SECURITY - FORCE MAJEURE - CONCEPT - RESALE OF THE BUTTER BY THE SUCCESSFUL TENDERER - FAILURE BY THE BUYER TO COMPLY WITH THE PROCESSING OBLIGATION - LOSS OF THE SECURITY PROVIDED BY THE SUCCESSFUL TENDERER ( REGULATION NO 232/75 OF THE COMMISSION , ART . 18 ( 2 ))