WCF Callback Implementation

Recently i developed the project in which i got the chance to explore WCF. Currently the project which i had developed implements the service and the Client. Service will send the recent status and other related data to client. Basically it is nothing but the one way communication. But the problem which i am facing now is when i am creating the two instance of the client then its giving me exception saying “Connection is already established”. So i was thinking of making the communication as Duplex using Callback implementation and swapping the current server and client implementation. Now my windows service will host the service and Windows Forms application will act as client, so that we can have multiple instance of the Client. Currently even i am doing some proof of concept on this topic. Please comment if there is any appropriate suggestion.
Rishi