Silverlight WCF + SSL security error - crossdomain.xml never requested

The problem was that I was missing clientaccesspolicy.xml. Having crossdomain.xml was not sufficient in this case. I think this is because the WCF invocation was not just cross-browser but also cross-protocol (the Silverlight app was served via http but the services were served via https).

In addition, my clientaccesspolicy.xml had to explicitly allow access for http as follows:

<?xml version="1.0" encoding="utf-8"?>  
<access-policy>  
    <cross-domain-access>  
        <policy>  
            <allow-from http-request-headers="SOAPAction">  
                <!-- IMPORTANT! Include these lines -->
                <domain uri="http://*"/>  
                <domain uri="https://*"/>  
            </allow-from>  
            <grant-to>  
                <resource path="/" include-subpaths="true"/>  
            </grant-to>  
        </policy>  
    </cross-domain-access>  
</access-policy>

It now works like a charm.

A couple of things that tripped me up along the way:

• My browser was caching clientaccesspolicy.xml and crossdomain.xml. I would have to clear my cache every time I changed one of those files or it wouldn't recognize the newer version, despite the fact that IIS is configured to prevent client caching of this file.
• The requests to clientaccesspolicy.xml and crossdomain.xml were not always showing up in Fiddler. I would often see CONNECT requests instead. I don't understand the reason for this but I've learned not to rely on Fiddler to confirm these requests are being made. Perhaps I have some rogue setting somewhere (it's not the "Decrypt HTTPS traffic" setting because I already disabled it).

I have the same error, when I try to make a call to my site over http and my service was over https it failed. This error occured because my ISS had no certificate, so, when the app tried to download the clientaccesspolicy, it failed.

Take a look in any debug tool on your browser and look for clientacccesspolicy file, then check that if it is being downloaded.