Many people ask question why polling duplex session shutdown after 10 minutes in spite of polling duplex InactivityTimeout value is more than hour.
In private email Christopher Scrosati (Silverlight WS Team) told me that I've also should configure ReciveTimout.
Here is the code sample, which shows how to configure polling duplex correctly:
HttpTransportBindingElement
http = new HttpTransportBindingElement();
BinaryMessageEncodingBindingElement
binary = new BinaryMessageEncodingBindingElement();
PollingDuplexBindingElement
polling = new PollingDuplexBindingElement();
polling.InactivityTimeout = TimeSpan.FromHours(1);
CustomBinding
binding = new CustomBinding(polling,
binary, http);
binding.ReceiveTimeout = TimeSpan.FromHours(1);
Hope it helps! Many thanks to Christopher =)