error : The underlying connection was closed: The connection was closed unexpectedly.

If the error

{"The underlying connection was closed: The connection was closed unexpectedly."}

blows up for some of the web service methods, while others work correctly, the reason may be the return objects refer to each other in a recursive manner. 

In my condition, i got the error while returning Sentence.

Paragraph() {

     List<Sentence> Sentence;

}

Sentence() {

  List<Paragraph> SomeText;

}

When the type of SomeText is changed from Paragraph  to Sentence, everything works fine!