Technical issues with Heroes III.

I'm a silly person, and I just couldn't find anything by searching the forum, and Google didn't give me anything useful.
The problem is that when I launch the game, it crashes with a message saying that there isn't enough disk space. Of course, there's plenty of free space.
I've tried changing the amount of free space on the disk, removing the game, and restarting – the error persists.
My question is, is it possible to fix this without reinstalling the game? Everything was working fine until today. It's an unpatched version, just the base game from the disc.

P.S. – When registering, the month and date of birth fields seem to treat March as a feminine noun, which is incorrect.

Thank you in advance for your answer.