Calorimetric, optical reflectivity and electron-diffraction measurements have been employed to investigate the nature of the smectic-A-crystal-B transition in thin free-standing 40.8 (N-4-n-butyloxybenzylidene)-4-n-octylaniline) films. The results from thin films shed an important light on previous results obtained from mechanical response investigations. Moreover, while the smectic-A-crystal-B transition of bulk 40.8 samples shows a strongly first order transition, the corresponding transition at the outermost layers exhibits pronounced fluctuations, indicating the remarkable effects of reduced dimensionality.