HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Um, is it okay that the autosave in single-player is password-protected, and the game can't recognize it later?

I changed the header from PROTECTED to a magic-header gzip, but the save file still doesn't work.
I suggest either adding a toggle to enable/disable password protection for saves, or disabling password protection for single-player altogether.