Application Pool shutting down
I just ran into this after upgrading my Win7 Ultimate x64 machine to SP1. The aforementioned message was found in the Application event log. It was accompanied by its good friend, "Application pool 'DefaultAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool." in the System event log.
I changed the advanced setting of the app pool, "Load User Profile" from True to False and my app pool is running again using the configured identity (which, in my case is a domain account).