How to troubleshoot the "503 Service Unavailable" error message in Outlook Web Access in Exchange Server 2003

After you type the address to Microsoft Outlook Web Access (OWA) on a Microsoft Exchange Server 2003 computer, you may receive the following error message in your browser before you receive the OWA log on prompt:

This problem occurs if the Davex.dll file cannot communicate with a mailbox store or with a public folder store.

Make sure that all the services are running

The "503 Service Unavailable" error message may occur if the Exchange 2003 services are not running, particularly if the System Attendant service and the Information Store service are not running. To view the services and make sure that all the services are running:

1. Click Start, point to Programs, point to Administrative Tools, and then click Services.
2. In Services, find Microsoft Exchange Information Store and Microsoft Exchange System Attendant under the Name column, and then look for Started under the Status column.
3. If a service is not started, right-click the service name, and then click Start.

Make sure that the services are running under the Local System account

The "503 Service Unavailable" error message may occur if the Exchange 2003 services are not running under the Local System account. To make sure that the services are running under the Local System account:

1. Open Services.
2. Under the Name column, find Microsoft Exchange Information Store and Microsoft Exchange System Attendant, and then look for Local System under the Log On As column.
3. If a service is not logged on under the Local System account:
   1. Right-click the service name, and then click Properties.
   2. Click the Log On tab, and then click Local System account under Log On As.
   3. Click OK.

Mount the mailbox stores and the public folder stores

The "503 Service Unavailable" error message may occur if the mailbox stores and the public folder stores that you want to gain access to are not mounted. Therefore, you must mount the mailbox stores and the public folder stores. To mount the mailbox stores and the public folder stores:

1. Click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. If the Display administrative groups option is turned on, expand Administrative Groups, and then expand First Administrative Group (where First Administrative Group is the name of your administrative group).
   Note To display administrative groups, right-click Your_Organization, click Properties, click to select the Display administrative groups check box, click OK two times, and then restart Exchange System Manager.
3. Expand Servers, expand Your_Exchange_Server_Name, and then expand First Storage Group.
4. Right-click Mailbox Store, click Mount Store, and then click OK.
5. Right-click Public Folder Store, click Mount Store, and then click OK.

See if a registry key that exceeds 259 characters exists in the HKEY_CLASSES_ROOT registry hive

The "503 Service Unavailable" error message may occur if a registry key that exceeds 259 characters exists in the HKEY_CLASSES_ROOT registry hive. During initialization, the Exchange OLE DB provider (ExOLEDB) scans the HKEY_CLASSES_ROOT hive to identify registered file types. If any subkey has a default value that exceeds 259 characters, or if there is a discretionary access control list that is not valid on one of the subkeys, ExOLEDB may quit unexpectedly.

If a subkey exceeds 259 characters, or if there is a discretionary access control list that is not valid, the following series of event ID messages are logged in the application event log when you restart the Exchange 2003 services: Additionally, the following event ID message may be logged in the application event log multiple times. The Free/Busy service may also generate some errors.The following event ID message may be logged in the system log multiple times:To help troubleshoot this issue, run the HKCRScan tool (HKCRScan.exe). The HKCRScan tool enumerates the HKEY_CLASSES_ROOT registry hive to locate subkeys that contain more than 259 characters. Additionally, HKCRScan helps determine if there is an invalid discretionary access control list by returning error code 0x5. This error code means "Access denied" when it enumerates a registry key. The HKCRScan tool is an internal tool developed by Microsoft. To obtain this tool, contact Microsoft Product Support Services (PSS). For additional information about how to contact PSS, visit the following Microsoft Web site:

See if a Group Policy object exists that prevents the MSExchangeIS service from initializing

The "503 Service Unavailable" error message may occur if a Group Policy object (GPO) exists that prevents the MSExchangeIS service from initializing.

You may notice event ID messages that are similar to the Event 101 EXOLEDB and the Event 9542 MSExchangeIS that this article describes.

Note The descriptions of the event ID messages may be different from those that are listed in this article.

You may also notice the following event ID messages:
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: To work around this issue:

1. Locate and export the following registry key to back it up:
   [HKEY_CLASSES_ROOT\AppID\{9DA0E0EA-86CE-11D1-8699-00C04FB98036}] "LocalService"="MSEXCHANGEIS"
2. Delete the following registry key:
   [HKEY_CLASSES_ROOT\AppID\{9DA0E0EA-86CE-11D1-8699-00C04FB98036}] "LocalService"="MSEXCHANGEIS"
3. Note You must complete step 2 before you continue to this step.
   
   In the DCOM Configuration utility (Dcomcnfg.exe), set the Identity tab on the ExOLEDB DCOM Service to The launching user:
   1. Click Start, click Run, type dcomcnfg, and then click OK.
   2. Expand Component Services, and then expand Computers.
      
      Note The Computers node may take several minutes to expand.
   3. Expand My Computer, and then expand DCOM Config.
      You receive the following message:
      The CLSID {9DA0E103-86CE-11D1-8699-00C04FB98036}, item C:\Program Files\Exchsrvr\bin\STORE.EXE and title Exoledb Session Factory has the named value AppID, but is not recorded under \\HKEY_CLASSES_ROOT\AppId. Do you with to record it?
   4. Click Yes.
   5. Under DCOM Config, right-click Exoledb Session Factory, and then click Properties.
      
      Important Exoledb Session Factory does not appear if you do not remove the registry key that is described in step 2. Additionally, when you click Properties, the Exoledb Session Factory Properties dialog box may take several minutes to appear.
   6. Click the Identity tab, click The launching user, and then click OK.
   If this procedure resolves the "503 Service Unavailable" error for OWA, the issue is related to a GPO. You may want to change or remove the GPO that is causing the issue. If this procedure does not resolve the "503 Service Unavailable" error, import the registry key that you exported and then deleted. Permanent removal of this registry key can cause other issues on the server if the issue is not related to a GPO.

Reregister the MDAC Components

If you view event ID 101 EXOLEDB messages and event ID 9542 MSExchangeIS messages such as the following event ID messages, some Microsoft Data Access Components (MDAC) may be incorrectly registered, and you must reregister them:
The following list contains the .dll files that you must have so that you can reregister the MDAC components to resolve this issue. You must stop the Information Store service before you reregister the files and then restart the Information Store service after you successfully reregister the following .dll files.

Note The Oledb32.dll file version must be 2.8.1022.0 or later.

• C:\Program Files\Common Files\System\Ole DB\Oledb32.dll
• C:\Program Files\Common Files\System\Ole DB\Oledb32r.dll
• C:\Program Files\Common Files\System\Ole DB\Msdaipp.dll
• C:\Program Files\Common Files\System\ado\Msado15.dll
• C:\Program Files\Common Files\System\Ole DB\Msdaurl.dll

To register a .dll file:

• Click Start, click Run, and then type regsvr32 followed by the path and name of the .dll file that you want to register. For example, to reregister the Oledb32.dll file, type the following command at the command prompt:
  regsvr32 "c:\program files\common files\system\ole db\oledb32.dll"

Note When you try to register one of these files, you may receive an error message that is similar to the following: For more information about this scenario, click the following article number to view the article in the Microsoft Knowledge Base:

Verify the permissions for the HKEY_CLASSES_ROOT registry key

The default permissions are as follows.