SilverLight3访问Wcf 时，定要加跨域文件(clientaccesspolicy.xml或者crossdomain.xml)

clientaccesspolicy.xml

<?xml version="1.0" encoding="utf-8"?>
<access-policy>
  <cross-domain-access>
    <policy>
      <allow-from http-request-headers="*">
        <domain uri="*"/>
      </allow-from>
      <grant-to>
        <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>
  </cross-domain-access>
</access-policy>

注意：一定要用 http-request-headers="*" 这个，否则不会成功

crossdomain.xml

<?xml version="1.0" encoding="utf-8" ?>
<cross-domain-policy>
  <allow-access-from domain="*" />
</cross-domain-policy>