I'm using the visualforce flash tag:

<apex:flash src="{!$Resource.FlashApplication}"
         id="CmpId"
         width="100%" height="100%"
         flashvars="session_id={!$Api.Session_ID}&server_url={!$Api.Partner_Server_URL_90}" />

However when loading the visualforce page the prompt "This page contains both secure and nonsecure items." appears.  When the  <apex:flash is commented out, the page loads without the prompt.

Any ideas?