Map won't open

Hi,

I recently made a map based on the old version of Brutal Slope.
It all began when I chanced the name of the map to describe it as acuarte as possible, so I did that.
But then realized, that I also had that useful program called BeamNG Map Options to do that for me. Then I saved the map, got out of the map editor, started the program, but it won't let me click next.
So I started up BeamNG again to check if something was wrong.

Yes indeed there was something wrong. An error message appeared saying: MissionGroup in *****.mis not found. I searched through the forums, but not many posts matched. Some said to verify the game cache. I did that multiple times, but it didn't work for me.
Some others said, it could be the game was pirated. But I bought the game 3 years ago, long before the game was on steam. Eventually I gave up. But now I'm here writing this thread.

Long story short, my question simply is:
How do I fix this problem?