I have experimented a lot of 1.44Mo floppy disk formated in 720Ko for my Atari. As 1.44Mo floppies are sold already formatted, it is hard to make them work good the first time you format them to 720Ko. That makes a lot of strange errors. So I allways format them at least twice or three times before using them. It prevents from magnetic field remanance of the 1.44Mo format deeply written on the floppy material. Could it be the same for hard disk if you don't use DOS format but GEM format ?