Before the RC release of MVC4/WebAPI JsonArray and JsonObject lived in System.Runtime.Serialization. Once you upgrade your project these options disappear.
The fix is pretty simple. In the latest RC release of MVC4/WebApi Microsoft switched the JSON handler to JSON.NET
The project should have a reference to Newtonsoft.Json (if it does not, you might need to load the NuGet package.
Once this is complete add a using statement
After that you can now use:
- JArray in place of JsonArray
- JObject in place of JsonObject
- so on and so forth.