 <p>The problem was with my properties. When I've omited <code>set</code>, I got this error...</p> <pre><code>[DataContract] public class YoloClassRO { private int k = 42; [DataMember] public int K { get { return k; } } } [DataContract] public class YoloClassRW { private int k = 42; [DataMember] public int K { get { return k; } set { k = value; } } } </code></pre> <p><code>YoloClassRW</code> - works</p> <p><code>YoloClassRO</code> - not</p> <p>Well described <a href="http://stackoverflow.com/questions/1873741/wcf-exposing-readonly-datamember-properties-without-set">Exposing readonly DataMember properties without set</a>.</p>