How to solve Siverlight application's 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?

An error occurred while trying to make a request to URI ‘http://localhost:<portnumber>/<ServiceAppName>/<serviceclassname>’. 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.

 When you call WCF Service using Silverlight you might receive the above error message.

 Here i am showing you how to solve this problem , which i have got so many times thanks to Chanmingman's blog from where i able to solve this.

The Steps to follow

1. Create an xml file using notepad and save as clientaccesspolicy.xml with the following content.

<?xml version="1.0" encoding="utf-8"?>

<access-policy>

  <cross-domain-access>

    <policy>

      <allow-from http-request-headers="SOAPAction">

        <domain uri="*"/>

      </allow-from>

      <grant-to>

        <resource path="/" include-subpaths="true"/>

      </grant-to>

    </policy>

  </cross-domain-access>

</access-policy>

2. Create an xml file using notepad and save as crossdomain.xml with the following content.

<?xml version="1.0"?>

<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">

<cross-domain-policy>

  <allow-http-request-headers-from domain="*" headers="SOAPAction,Content-Type"/>

</cross-domain-policy>

3. Copy these 2 files into web site root folder for example, c:\inetpub\wwwroot. for your IIS 

Cheers :)