WCF method called twice

Question

I have a web service which is returning data to the desktop application. The problem I am having is, when the web service returns small volume of data everything works fine but

Answer 1

I also had this problem and my solution was similar to Batgar's, but with a twist. I had a class that had a property of type object. I had to add KnownType attributes to the class for every type the object could hold. I couldn't populate the KnownType on-the-fly as the class didn't know what the object will contain.