Two possible causes of the problem:
1) The path to the map or the map name contains Cyrillic characters. To avoid this problem, replace all Cyrillic characters with Latin characters.
2) The path to the map is too long (e.g., C:\Program Files\Nival Interactive\Heroes of Might and Magic V\Heroes of Might and Magic V\Heroes of Might and Magic V\Heroes of Might and Magic V\Maps). Solution: shorten the path as much as possible.

Please read the forum more carefully.

Added 2 minutes later
Hello everyone.
1. Can I change the size of an already created map (e.g., from small to medium) or copy a part of it?
2. Which of the creature parameters (placed on the map) is responsible for the presence of upgraded creatures (e.g., there are golems, and among them there are also steel golems)?
Thank you in advance.