KyoKusanagi , was the previous working firmware v3.5.37?
If that's the case, then your player could be compatible for v3.5.35 or v3.5.37. Which can be found:
v3.5.35
http://www.mympxplayer.org/actions-3535-dc15.html
v3.5.37
http://www.mympxplayer.org/actions-3537-dc16.html
You'll need to try all the firmwares for your screen size (1.5" in this case) until you get one working fully with your player.
The Success message shown on the Upgrade Tool only tells you that the firmware has been successfully flashed into the player. It does not tell whether it is compatible with your player or not.
You don't need any other external files for the player operate, besides the firmware file.