Disk System needs better calibration.
I'd tried to calibrate the spindle for about 1 hour without success. At last, when I lost all hope, I decided to tighten the screw and keep my FDS on a shelf as a decoration piece. But before, I needed to try it once more... AND IT WORKS!
I screamed happily, running through my house like crazy!
I think I had luck!
Maybe that's the reason.
I can add, that Metroid is a more difficult disk because it loads so much.