When I load a saved game, I get an error – I deleted the file and then restored it.

That’s not right! Files from that server can’t be downloaded (where did you even find it? Have you not heard of normal file-sharing services or Google/Yandex Drive or Mail.ru Cloud?), but the main thing is: you can attach files to a message here (in extended mode).
Regarding the version error: you are probably opening a map or save file made in HotA in the regular "Heroes 3". Therefore, you need HotA and the map editor for it.
And also: I still downloaded one file from there, random_map_12.h3m, but its format doesn’t look like map files for "Heroes". So, maybe the files are simply corrupted. Or... wait, if you created them in the game using the HD mod, then they are ENCRYPTED! To decrypt them, you need to enter the passwords of all players.