Our Exchange 2007 CAS server recently logged with an IIS deadlock error.

Event Type: Warning
Event Source: W3SVC-WP
Event Category: None
Event ID: 2262
Description: ISAPI ‘C:\WINNT\Microsoft.NET\Framework\v2.0.50727\aspnet_isapi.dll’ reported itself as unhealthy for the following reason: ‘Deadlock detected’.

All of our users weren’t able to access their emails with OWA or Outlook clients. The only solution was to restart all of our Exchange servers so that our users can temporary access their emails until we find a fix for it.

Later, we upgraded all of our Exchange 2007 servers to the latest service pack (Exchange 2007 SP2). So far there was no deadlock error showing on the Event logs and users haven’t experienced any issues logging in.