I encountered an interesting problems today.  I was trying to setup a Silverlight application to run over https.  I was able to successfully run it over HTTP prior to this task.  However, when I switched URL to https://www.mysite.com, I got the error 2104 “Could not download the Silverlight application”.  The solution that I had to experiment with to discover (Google was not help) was setting expiration time to 1 minute.  It worked perfectly fine with expire immediately setting for http protocol, but not https.