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Quick fix
I've just tried this with the latest version of the game, and my result is the same. I also can't start a new campaign. You are correct. If anyone bricks their game this way, know that the easiest solution is to close the game, start a new one, go to campaign and click "delete chosen" and then one by one delete each of the 27 suntorn dawn chosen. After that the game does not seem to have any ways that it locks up.
Bug reproduction
I think with the new changes, there's something that changed with rosters // characters that it can't start with the file as it was created back then. I've also tried exporting it to a new file, and then importing it, but it still wouldn't start.
I think it's because a new update added more information to characters, physical traits, their entry transformation and relationship restrictions.
Solving it by my hand
It means I'll have to recreate the roster from scratch, which took me about 8 hours or so last time. I also don't know if
CSdev has left any guide on transformation ID#'s or if I'll have backward engineer to learn that new system. I've noticed that the game also locks up if you try to edit any of the old character files with the latest build.
Solving it with CSdev help
Ideally
CSdev would add some lines of code that when chosen are edited, that if they miss any of the new types of data (physical traits/entry transform/relationship restriction), that instead of locking up, it would create a default values of that data for those characters, so that I could use the program to recreate the chosen with the new types of data so that it would work again. But that might be asking a lot of him and I'm sure he's quite busy already.
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It's by pure chance that I saw this thread and post, I don't frequent here often anymore. I'll try and check up within a week and see if there's help from
CSdev or not. If he does, I'll fix it asap. If he doesn't, I might or might not fix it because it will eat up quite some of my time starting over again.