The mainstream theory of economics is receiving frequent criticism from its opponents and from its followers. Surprisingly (and precisely for that reason), the most serious criticism - arguing that many of the theory's models are not logically closed - was formulated by F. Hahn himself, co-author/co-editor of General Competitive Analysis and Handbook of Monetary Economics: the price of money can be at zero equilibrium. The study examines the negative outcome and consequences of this contribution, which has become known as the Hahn Problem.