Got the same error message while trying to activate league system of Bosnia & Herzegovina.
At the start, I made the basic rules in Basic editor and it worked well, with no problems. After that I converted the file to Advanced editor. With advanced rules the verification in editor went through without any problems. But, in the game, the same "Rule Group has empty discipline rules" error.
Of course, I can create the game and play the first season. But after the first season I get crash dump and there's no way to get into second season.
There are problems with Discipline rules.
Here are the rules with the advanced rules (the file with a problem)
And here are the rules with basic rules only (that file is working)