Originally posted on our forums here.
Hello friends!
In the most recent patch, we upgraded the version of Unity that the game is running on, which resulted in the .net runtime being upgraded as well.
The most acute result of this is that any mod solutions will have to be updated to target the 4.0 framework. (In Visual Studio, this is in the project properties, Application > Target Framework.) This will fix compilation issues caused by the patch.
The framework upgrade was an unintended side-effect of upgrading Unity, and we didn't do a good job of notifying you in the mod community what was going on. I'm sorry about that. Hopefully we don't have an upgrade like this again, but if we do I'll be more attentive!
For questions/feedback please visit the official forums: https://forums.kleientertainment.com/forums/topic/115509-net-framework-updated-to-40/