Tess Ferrandez takes a debugging look at what happens when you fail to close client proxies in a timely manner. Given the relatively long default time before the server idles out a client (10 minutes) and given the relatively small default number of connected clients (10), this is probably one of the most frequently encountered issues for new WCF developers. You'll pretty much always want to adjust these settings in a production environment in addition to making clients close their connections more quickly.