Flash Builder 4 Security Error Accessing Url Destination: DefaultHTTP

I have built a FB4 application which accesses a .NET web service of a partner company. The app runs just fine in FB4 development environment, but won't work when published to my server. I can not figure out how to get past the following error: Security error accessing url Destination: DefaultHTTP It is unlikely that I will get a crossdomain.xml file on their server, so I'm trying to get it to work using a proxy. The proxy.php is located in the same directory as the swf, and it works just fine if I use it directly in the browser.

The following is what I currently have setup:

proxy.php:
<?php
$session = curl_init(trim(urldecode($_GET['url']))); // Open the Curl session
curl_setopt($session, CURLOPT_HEADER, false); // Don't return HTTP headers
curl_setopt($session, CURLOPT_RETURNTRANSFER, true); // Do return the contents of the call

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