Hey I've been lurking this thread since I started getting error code 13's.
I'm not very good with the technical side of this issue, however I'll fill you in on what I've noticed and I hope it helps.

I used to have all the store items installed in my game, and played Riverview- error code 13. So I reinstalled my game and patched with v1.2.7. I installed the Indiestone mod and full store content and Riverview. Played Sunset Valley- error coder 13.

Finally I reinstalled the game patched again with V1.2.7 and installed the Indiestone mod. I did not install store content or Riverview.

I have now been happily playing for 2 weeks with no error code, as to before when I occurred them within the first three days.

Steele mentioned that it may be a problem with custom content, and from what I've experienced it was.

Hope that helps, sorry I can't be more technical.

Great to see you guys working on the problem