Got this strange error today while using Roslyn via NuGet.
To fix it check this:
- The is not outdated version of the "Roslyn.Services.dll" process running (check task manager)
- The platform target of your DLL or application is "Any CPU"
- Visual Studio 2012: Disable "Prefer 32-bit" under the "Platform target" drop-down menu for your startup project.
This was the reason why it was not working for me.