This error happens in interactive mode only, not when using he --render option:

TrifleJS.exe
Unhandled Exception: System.IO.FileLoadException: Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.
at TrifleJS.Program.Interactive()
at TrifleJS.Program.Main(String[] args) in c:...\trifleJS\Program.cs:line 88

I'm using Visual Studio 2013, the project was converted automatically. The .Net target for the solution is 4. I couldn't figure out which assembly has been compiled for .Net 2.