One of my side projects is working on a Windows Home Server (WHS) add-in to allow remote access to all of my music and photos. I recently upgraded my WHS server to Windows Media Player 11 (WMP11) so that I could access photos on the server from my new i-mate Momento 70 wireless digital picture frame which only supports WMP11. Note that WMP11 is not officially supported on WHS but it seems to work just fine once you trick it into installing.
After doing the upgrade I immediately ran my add-in application to see if it still worked and of course...it didn't. The application started throwing the following error:
Exception from HRESULT: 0x00403C9
It turns out that this is an "Access Denied" error due to the user I was running the app under not being allowed access to my shared media. To solve the problem I simply had to go to Options->Library->Configure Sharing in WMP11 and allow access to the "Other users of this PC" group.