"Open save game with editor
Search for the capital
Its an entry with a number and there is smething like this [Owner]=BAR or something similar."
Make sure to add an entry that states when you "took it over". I had this exact same thing happen. I had a peasant rabble in Numidia land turn into Terra Incognito and crash the game. The fix was the same. Here's an example of what to add, I'll use Nervii as the example:
Change:
}
owner="BAR"
controller="BAR"
To:
}
owner="ROM"
controller="ROM"
Then, at the bottom, change:
}
511.12.7={
owner="BAR"
}
537.1.1={
add_core="BAR"
To:
}
511.12.7={
owner="BAR"
}
537.1.1={
add_core="BAR"
}
580.11.19={
controller="ROM"
}
Just make sure the year (580 in this case) is PRIOR to the current game year.
And I always rename it "test.Rome" first just in case.