WCF Error in Silverlight

I am trying to use silverlight to create an application that uses a SQL Database on a remote server.

It seems things work fine up to a point. Suddenly with the creation of 1 more public function in the WCF I get the following error;

An error occurred while trying to make a request to URI 'http://localhost:2309/Service1.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 have tried everything I can possibly think of to get aroung this. Does anyone have any ideas.

Thanks
Pete