From now all upcoming releases of MatriX for Silverlight will be compiled against Silverlight 4 because of improvements in the security policy system.

Since Silverlight 4 a connection request using sockets can choose to retrieve the policy file via the HTTP protocol on TCP port 80 instead of the custom TCP protocol on port 943. Web servers are already running in mosts environments. This makes your setup much easier because you don’t need the special policy server on port 943.

To enable policy download over HTTP use the following code in the latest MatriX for Silverlight version.

XmppClient.DownloadClientAccessPolicyViaHttp = true;

You can read more details about the Network Security Access Restrictions in Silverlight here in the MSDN