I created a WCF service and I planned to consume this in a Silverlight application. So I created the WCF service in the Website host project. The service is a simple WCF service that only returns a number - something like a Hello World WCF-SL. So after adding a service reference in the silverlight client project to the Service URI, after calling async the service method (by using the generated proxy), I get the following exception in the callback method:

An error occurred while trying to make a request to URI 'http://localhost:4566/SLService.svc'. This could be due to attempting to access a service in a cross-domain way without a proper cross-domain policy in place, or a policy that is unsuitable for SOAP services. You may need to contact the owner of the service to publish a cross-domain policy file and to ensure it allows SOAP-related HTTP headers to be sent. This error may also be caused by using internal types in the web service proxy without using the InternalsVisibleToAttribute attribute. Please see the inner exception for more details.

I only created a HelloWorld WCF service with nothing else but a simple method that returns a dumb number and it's hosted on my locally. Must I have clientaccesspolicy.xml or crossdomain.xml? I acces my service locally. Every time I create a new simple/dumb WCF-SL solution, I get this error. I use VS2010 and Silverlight 4. I cannot get a simple/dumb WCF-SL solution working locally. Is there something wrong with the configuration? On another machine in the same network, it does work properly, so I assume something is misconfigured. Any thoughts?