<p>In a silverlight application, I want to access the page the silverlight .xap file from an HTTP subdomain, but have the web services access a different subdomain for sensitive information over HTTPS.</p>

<p>I set up clientaccesspolicy.xml at the root of the subdomain and it lets the silverlight app access its services over http, but not over https.  It gives the cross domain access error that it would give normally without a clientaccesspolicy in place.</p>

<p>I know that browsers themselves have a lot of restrictions about mixing http and https.  Am I trying to do something that is not allowed?  </p>

Check out:
http://silverlight.net/forums/t/12741.aspx
You can either make https calls to the
  same domain or http cross-domain
  calls, but not https cross-domain
  calls.
This is described in
http://msdn2.microsoft.com/en-us/library/cc189008(VS.95).aspx
(see "If not HTTPS" in the matrix)
  By JohnSpurlock