No, I'm not that clueless about scripts.
Here's the full file path:
('/Maps/SingleMissions/NewRandomMap21/CombatScript.xdb#xpointer(/Script)')
It's strange, but it seems like the path is incorrect:
SetHeroCombatScript(hero1, '/CombatScript.xdb#xpointer(/Script)')
Here's an example of what the map archive should look like.