Separating Out A Wcf Service, Server, And Client

I have a solution in VS 2010: a WCF Service Library project ("NotifyService") and two Windows Forms projects, one for a server ("NotifyServer")and one for a client ("NotifyClient"). My goal is to have a duplex WCF service that will notify any number of connected clients when the server pushes out a notification. The clients do not need to communicate to the server except to subscribe and unsubscribe from the server's updates. However I seem to be running into problems nailing down the InstanceContext.

Here's the code for the WCF service:

<ServiceContract(
CallbackContract:=GetType(INotifyCallback),
SessionMode:=SessionMode.Required)>

[Code].....

Since I'm setting everything up through code, there are no app.config files. The problem I'm having is that my Subscribe method is never called. When debugging, I get an error after stepping through that line (not an exception) that says "Unable to automatically step into the server. The debugger failed to stop in the server process." When I go back to my server form and click the button designed to raise an event on the callback clients, it steps into the NotifyService class but the _callbacks list is empty, meaning the Subscribe method either never ran, or it never ran on that instance.

I have fought with this for almost a week. This is nearly an identical copy, at least on the service-side, to what was described here, and I've compiled that and it works.