If your web services are running on a server that is not in the DMZ and you are not able to open port 80 to these services either then you will encounter a common scenario. Your Silverlight application will not be able to connect to these services because it can’t get to the clientaccesspolicy.xml file that is required to access services on a different server to the one that served your Silverlight application.

If you hosting your Silverlight application on a machine running IIS 7.5 (Windows Server 2008) then help is at hand – click here for more details.