C# Parsing JSON data within Mobile project OR via Controller Issue

When I invoke the following to a custom controller to return data to my client (Windows Phone 8.1 app):

var _lines = await App.MobileService.InvokeApiAsync<List<Tfl.Api.Presentation.Entities.Line>>("lines", System.Net.Http.HttpMethod.Get, new Dictionary<string, string>
            {
                {"url", "http://ift.tt/19qNGRY;}
            });

I received the following Exception:-

FileNotFoundException was caught 
Could not load file or assembly 'System.Runtime.Serialization, 
Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one 
of its dependencies. The system cannot find the file specified.

However, I successfully parse the JSON data via the controller [I did have an image here displaying the data, but not enough rep to post!] and I also have no references to the above dll in my Windows Phone application.

Any ideas?

Note: Occurs using either local parsing within the mobile app or via controllers in a service app; also running VS Ultimate 2013 with Update 4