On an Internet Information Services (IIS) 7.0 server, you may see one or more of the following symptoms. In the system event log, you may see one or more occurrences of event ID 2297 from source Microsoft-Windows-IIS-W3SVC-WP and event ID 5172 from source Microsoft-Windows-WAS that resemble the following.
Performing an IISRESET enables your Web sites to serve requests again.
Message 1
Message 2
Additionally, client requests may receive a response with status code 503 "Service unavailable." You may see entries in the HTTP error logs with a status of "AppOffline."Performing an IISRESET enables your Web sites to serve requests again.