Error 503 Service Unavailable when you browse Windows SBS websites

Generally, this error occurs if the application pool that is associated with the web application doesn't start. To troubleshoot this issue, follow these steps:

1. In Event Viewer, view the System log to find errors from the Microsoft-Windows-WAS source. An event is frequently logged in the System log if the application pool fails to start.
2. If you don't find any relevant events in the System log, search for relevant entries in the HTTPERR log file. The httperr1.log file is located in the following system folder:
   c:\windows\system32\logfiles
   In the file, search on "503" to locate any relevant information about why the application pool failed. For example, you may see an entry that resembles the following:
   2011-12-08 18:26:42 ::1%0 6721 ::1%0 443 HTTP/1.1 GET /owa 503 3 N/A SharePoint+Web+Services+Root
   The log entry should list the site you are trying to browse and the application pool that is being used. Make sure that the correct application pool is being used for the site.

For example, you try to browse the "/owa" website by using the Sharepoint Web Services Root application pool. The OWA application is supposed to use the MSExchangeOWAAppPool application pool. However, there is a misconfiguration in Internet Information Services (IIS). To resolve this issue, you would check the Application Pool for the site and for the site bindings to make sure that IIS is configured correctly.

1. Open IIS Manager MMC. To start IIS Manager from the Administrative Services console, follow these steps:
   1. On the Start menu, click All Programs, click Accessories, and then click Run.
   2. In the Run text box, type control panel, and then click OK.
   3. In the Control Panel window, click Classic View, and then double-click Administrative Tools.
   4. In the Administrative Tools window, double-click Internet Information Services.
2. Check the bindings for each of the websites to make sure that they match the default settings in the following table.

   Website	Type	Host Name	Port	IP Address	Binding Information
   Companyweb	http	Companyweb	80	*	Port 80
   Default Website	HTTP http net.tcp net.pipe net.msmq msmq.formatname https https		80 80 443 443	* 127.0.0.1 * 127.0.0.1	808:* * Localhost localhost
   SBS Client Deployment Applications	http http	SBSConectComputer	80	*	*:80:connect
   SBS SharePoint	https		987	*
   SharePoint Central Administration v4	http		18000

3. Check each Application Pool value to make sure that the settings are correct. The following table contains the default settings for the standard SBS application pools.

   Application Pool	.NET Framework Version	Identity	Associated Applications
   DefaultAppPool	V2.0	ApplicationPoolIdentity	/rpc /rpcwithcert
   MSExchangeAutodiscoverAppPool	V2.0	LocalSystem	/Autodiscover /Autodiscover/bin /Autodiscover/help
   MSExchangeECPAppPool	V2.0	LocalSystem	/ecp
   MSExchangeOWAAppPool	V2.0	LocalSystem	/owa
   MSExchangeOWACalendarAppPool	V2.0	LocalSystem	/owa/Calendar
   MSExchangePowerShellAppPool	V2.0	LocalSystem	/PowerShell
   MSExchangeSyncAppPool	V2.0	LocalSystem	/Microsoft-Server-ActiveSync
   MSExchangeServicesAppPool	V2.0	LocalSystem	/EWS /EWS/bin
   SBS Sharepoint AppPool	V2.0	<Domainname>\spwebapp	Root Application for SBS SharePoint Root Application for Companyweb
   SBS Web Applications application pool	V4.o	NetworkService	/webhelp Root Application for Default Website
   SBS Web Workplace AppPool	V4.0	NetworkService	/Remote

The following documented issues commonly cause an HTTP 503 "service unavailable" error.

Issue 1: SharePoint AppPool identity is invalid

Description: Browsing SharePoint fails and the system event log records the following error:

Log Name: System
Source: Microsoft-Windows-WAS
Event ID: 5057
Level: Warning
Computer: server.domain.local
Description: Application pool SBS Sharepoint AppPool has been disabled. Windows Process Activation Service (WAS) did not create a worker process to serve the application pool because the application pool identity is invalid.

Resolution: Use the steps in the following blog post to resolve the issue: Issue 2: Access denied on Exchange SQM files

Description: Browsing SharePoint fails, and the following events IDs are recorded.

The System log includes the following event entry:

Log Name: System
Source: Microsoft-Windows-WAS
Event ID: 5022
Level: Warning
Computer: SERVER.contoso.local
Description:
The Windows Process Activation Service failed to create a worker process for the application pool 'SBS Sharepoint AppPool'. The data field contains the error number.

The Application log includes the following event entry:

Log Name: Application
Source: Microsoft-Windows-User Profiles General
Event ID: 1509
Level: Warning
User: CONTOSO\spwebapp
Computer: SERVER.contoso.local

Description:
Windows cannot copy file C:\Users\Default\AppData\Local\Microsoft\Exchange Server\v14\Configuration14400_100.sqm to location C:\Users\TEMP.CONTOSO.005\AppData\Local\Microsoft\Exchange Server\v14\Configuration14400_100.sqm. This error may be caused by network problems or insufficient security rights. 

DETAIL - Access is denied.

Resolution: Use the steps in the following blog post to resolve the issue: Issue 3: Application pool is enabled for 32-bit applications

Description: Browsing any website, such as /remote or /owa, may fail and generate HTTP error 503: "service unavailable"; or, the page may not load, and may appear to just hang.

The Application log includes the following error entry:

Source: Microsoft-Windows-IIS-W3SVC-WP
Event ID: 2282
Level: Error
Description:
The Module DLL 'C:\Program Files\Microsoft\Exchange Server\V14\Bin\kerbauth.dll' could not be loaded because of a configuration problem. The current configuration only supports loading images built for a x86 processor architecture. The data field contains the error number. 
Resolution: The error occurs if the application pool is set to enable 32-bit applications but is not configured correctly. By default, 32-bit support is disabled on the application pools. If 32-bit support is not required, check the advanced settings of each application pool to make sure that the Enable 32-bit applications value is set to False.



If 32-bit applications are required, use the steps in the following blog post to enable 32-bit application support correctly: