Consume soap web service with Xamarin.Forms

Hello,

I'm using Xamarin Studio on Windows to make an Android app(Portable Xamarin.Forms project). I'm trying to consume a web service using the guide at this page: http://developer.xamarin.com/guides/cross-platform/application_fundamentals/web_services/ in section "Consuming SOAP Services".

However, I can't seem to make it work at all. I can generate the proxy successfully(using this public url: http://wsf.cdyne.com/WeatherWS/Weather.asmx for testing purposes). A new file called "Reference.cs" is generated.

But the file Reference.cs generates several compile errors:

Error CS0234: The type or namespace name 'IExtensibleDataObject' does not exist in the namespace 'System.Runtime.Serialization' (are you missing an assembly reference?) (CS0234) (XamarinFormsTutorial)

.. and 41 others(all CS0234)

Anybody got an idea what is going on?