Classic AppPool will not stay running and presents errors within the Windows Application Event log.
The Windows Process Activation Service failed to generate an application pool config file for application pool
Also various Event ID's such as 5189 will appear in the Windows Application Event Logs
This is a known issue with IIS. Microsoft has presented a solution for this issue.
Follow the steps as outlined at the following website.
http://technet.microsoft.com/en-us/library/cc734988(v=ws.10)