LC
Its actually quite strange. I had the CTD (no error messages) several times when trying to add the extra province. Then yesterday I was moving provinces around and renaming and found I had the duplicate in the mercenaries.txt file. Today I thought I'd just try adding a new province in again and it worked first time. I then tried to add in some duplicated provinces into the mercenaries and couldn't get a CTD. I then thought it may be tied to features somehow as I think I had always tested with the land bridges in and didn't have any now. I added a land bridge and still couldn't get a CTD.

I then tried changing a sea colour for a lake to the one used in vanilla for lakes - and got an unexplained error but no direct CTD - so you couldn't now have 2 sea colours.

I then thought I'd try adding one more region and I got the straight CTD again. Which resolved itself once I took out a different region.

I really don't know what I did to not be able to add in the 199th originally. I'm sure I used different colours for different attempts. I also recall I accidentally started with a different sea colour to the main sea one in vanilla so maybe that had something to do with it.

My map is a British isles map so its completely new.