I have a web app that uses an installed certificate to send a web request to a 3rd party web service. This has worked for a long time on Windows Server 2003, but just recently we found a problem with it on 2008 installations. When logged into the server as the same user the App Pool uses, either locally or via remote desktop, the web app and it's secure 3rd party request works fine. However, when there are no user sessions open, the 3rd party request fails, as if the certificate were not attached to the web request. Any ideas?