This phenomenon usually comes as a result of incorrect floppy format. The S1000/S1100 had a peculiar feature of being able to format DD floppies to High Density (and the other way round). This was before the days of drives which could differentiate between the two. Although this was great at four in the morning when all you had was a handful of DD's and too much stuff in memory to fit onto them, formatting a low density disk to high will render it incompatible with the more recent samplers.