The MSExchangeSyncAppPool application pool crashes on a server that hosts a Microsoft Exchange Server 2007 Client Access Server role. If the default rapid-fail protection setting is used, the application is disabled after the crash occurs 5 times within five minutes. Therefore, the Exchange ActiveSync functionality becomes unavailable until the World Wide Web Publishing Service restarts.

When this problem occurs, the following events are logged in the System log:

Event ID 1011

Event Type: Warning
Event Source: W3SVC
Event Category: None
Event ID: 1011
Description:
A process serving application pool 'MSExchangeSyncAppPool' suffered a fatal communication error with the World Wide Web publishing Service. The process id was '<process id>'. The data field contains the error number.

Event ID 1009

Event Type: Warning
Event Source: W3SVC
Event Category: None
Event ID: 1009
Description:
A process serving application pool 'MSExchangeSyncAppPool' terminated unexpectedly. The process id was '1948'. The process exit code was '0x1'.

Event ID 1002

Event Type: Error
Event Source: W3SVC
Event Category: None
Event ID: 1002
Description:
Application pool 'MSExchangeSyncAppPool' is being automatically disabled due to a series of failures in the process(es) serving that application pool.

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To resolve this problem, install Update Rollup 2 for Microsoft Exchange Server 2007 Service Pack 1. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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To verify the rapid-fail protection setting of the MSExchangeSyncAppPool application pool, follow these steps:

1.	Open the Internet Information Services (IIS) Manager console.
2.	In the console tree, expand Internet Information Services, expand the node that corresponds to the server name, and then click Application Pools.
3.	In the details pane, right-click MSExchangeSyncAppPool, and then click Properties.
4.	On the Health tab, check the settings under the Enable rapid-fail protection section.

For more information about application pool health in Internet Information Service 6.0, visit the following Microsoft TechNet Web site:This problem generates a stack output that resembles the following.

Exception type: System.IO.IOException
Exception message: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
Exception level: 0
Exception stack trace: at System.Net.ConnectStream.EndRead(IAsyncResult asyncResult)
at Microsoft.Exchange.AirSync.ProxyHandler.BackEndReadContent(IAsyncResult asynchronousResult)
Inner exception follows...
Exception type: System.Net.Sockets.SocketException
Exception message: An existing connection was forcibly closed by the remote host
Exception level: 1
Exception stack trace: at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)

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