Getting this exception only when loading an existing game in KSP 1.3.1:
LOG 02:02:28.608] [PlayYourWay]: The runtime is already installed (OK).
[EXC 02:02:28.608] TypeLoadException: Could not load type 'System.Func`2' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
PlayYourWay.PlayYourWayScenarioInjector.Start ()
Reproduction: start game, create new save, go back to main menu, load the game you just created. It also shows up when loading this savegame in a new session.
Installed mods: Modulemanager and Play Your Way
KSP.log
Possibly related issue