I usually extract game files into a folder that I made for the game. It worked when I had the 0.8.2b version but then the game got accidentally deleted when I was cleaning unnecessary files off of my PC. I had to download the 0.8.2c version, and now thunderstore just will not let me change the game folder.
You have the directory set correctly. It would appear you have the same issue I did a while back. You're not doing anything wrong, but it's the mods that are causing the problem.
Some mods haven't been updated for this new version and whatnot. Check the date on when the latest update came out, then check the dates for your mods. Anything before will probably just crash you. Use up-to-date mods, and see if that fixes your issue. It fixed it for me.
If that doesn't fix it, I will try to further research your error, and see what I can find.