Hi! Glad you are enjoying the game. I am not 100% sure what causes the issue, but I'd check if the game's folder and/or the files inside are set to "read only", try to set the .exe of the game to run as an administrator, and if neither of those work you might try to move the game to a folder that likely doesn't have any access restrictions (like "documents") and see if that changes anything.
Let me know if one of these fixes the issue for you.