HOW TO: Troubleshoot the "503 Service Unavailable" Error Message in Outlook
Web Access 2003

For a Microsoft Exchange 2000 Server version of this article, see 257265.

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base: 256986 Description of the Microsoft Windows Registry

IN THIS TASK SUMMARY
Make Sure That All the Services Are Running
Make Sure That the Services Are Running Under the Local System
Mount the Mailbox Stores and the Public Folder Stores
See If a Registry Key That Exceeds 259 Characters Exists in the HKEY_CLASSES_ROOT Registry Hive
Notice That a Group Policy Object Exists That Restricts the MSExchangeIS Service from Initializing

SUMMARY
After you type the address to Microsoft Outlook Web Access (OWA) on an Exchange 2003 computer, you may receive the following error message on your browser before you receive the OWA log on prompt: 503 Service Unavailable
This problem occurs if the Davex.dll file cannot communicate with either a mailbox store or 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 and the information store 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, under the Name column, find Microsoft Exchange Information Store and Microsoft Exchange System Attendant, and then look for Started under the Status column.
3. If a service is not started, right-click the name, and then click Start.
Make Sure That the Services Are Running Under the Local System
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 under the Log On 3. As column, look for Local System.
A. If the service is not logged on under the local system account:
B. Right-click the service name, and then click Properties.
C. Click the Log On tab, and then under Log On As, click Local System account.
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: Event Type: Information
Event Source: MSExchangeSA Event Category: General
Event ID: 9014
Description:
Microsoft Exchange System Attendant has been started for Exchange server servername successfully.
Event Type: Information
Event Source: MSExchangeSA
Event Category: Monitoring
Event ID: 9095
Description:
The MAD Monitoring thread is initializing.
Event Type: Information
Event Source: MSExchangeSA
Event Category: Monitoring
Event ID: 9096
Description:
The MAD Monitoring thread is initialized.
Event Type: Information
Event Source: EXOLEDB
Event ID: 101
Description:
Microsoft Exchange OLEDB has successfully shutdown.
Event Type: Error
Event Source: MSExchangeIS
Event ID: 9542
Description:
Initialization of external interface OLEDB failed; Error ecServerOOM.
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.
Event Type: Error
Event Source: EXCDO
Event Category: General
Event ID: 8206
Description:
Calendaring agent failed with error code 0x800XXXXX while saving appointment.
The following event ID message may be logged in the System Log multiple times:
Event Type: Error
Event Source: DCOM
Event Category: None
Event ID: 10002
Description:
Access denied attempting to launch a DCOM Server. The server is: {9DA0E106-86CE-11D1-8699-
00C04FB98036} The user is SYSTEM/NT AUTHORITY, SID=S-1-5-18
Notice That a Group Policy Object Exists That Restricts the MSExchangeIS Service from Initializing
The "503 Service Unavailable" error message may occur if a Group Policy object (GPO) exists that restricts
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:
Event Type: Error
Event Source: EXCDO
Event ID: 8208
Description:
Calendaring agent failed with error code 0x8000ffff while expanding recurring appointments.
-and-
Event Type: Error
Event Source: DCOM
Event ID: 10009
Description:
DCOM was unable to communicate with the computer RCC-EXH-02-W using any of the configured protocols.
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk. To work around this issue:
1. Export the following registry key for back 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:
A. Click Start, click Run, type dcomcnfg, and then click OK.
B. On the Applications tab, in the Applications list, click Exoledb Session Factory, and then click Properties.
C. Click the Identity tab, click The launching user, and then click OK two times.
If this workaround 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 these steps do 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.
4. If you view 101 EXOLEDB event ID messages and 9542 MSExchangeIS event ID messages such as the following event ID messages, some Microsoft Data Access Components (MDAC) may be incorrectly registered, and you must reregister them:
Event Type: Information
Event Source: EXOLEDB
Event ID: 101
Description:
Microsoft Exchange OLEDB has successfully shutdown.
-and-
Event Type: Error
Event Source: MSExchangeIS
Event ID: 9542
Description:
Initialization of external interface OLEDB failed; Error Unknown error.
The following list is a list of 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:
C:\Program Files\Common Files\System\Ole DB\Oledb32.dll
C:\Program Files\Common Files\System\Ole DB\Oledb32r.dll
C:\PROGRA~1\COMMON~1\System\OLEDB~1\Msdaipp.dll
C:\Program Files\Common Files\System\ado\Msado15.dll
C:\PROGRA~1\COMMON~1\System\OLEDB~1\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~1\common~1\system\oledb~1\oledb32.dll