Exchange Server 2007 mailbox users cannot retrieve the free/busy information for Exchange Server 2003 mailbox users in a large Exchange Server organization that has more than 100 administrative groups

You have a large Microsoft Exchange Server organization that has more than 100 administrative groups. The Exchange Server organization includes Microsoft Exchange Server 2007 servers and Microsoft Exchange Server 2003 servers. In this situation, Exchange Server 2007 mailbox users cannot retrieve the free/busy information for Exchange Server 2003 mailbox users. Additionally, the following events are logged in the Application log.

Event ID 4003

Event Type: Error
Event Source: MSExchange Availability
Event Category: Availability Service
Event ID: 4003
Description:
Process xxxx[w3wp.exe:/LM/W3SVC/1/ROOT/xxxx]:
Microsoft.Exchange.InfoWorker.Common.Availability.PublicFolderRequest failed. The exception returned is Microsoft.Exchange.InfoWorker.Common.Availability.PublicFolderRequestProcessingException: The request was aborted: The request was canceled.. The request information is <xxxxxxxx>.. The Availability service could not successfully retrieve Schedule+ free/busy data for one or more legacy Exchange mailboxes. To find the root cause of this error, increase the diagnostic logging level of the MSExchange Availability service.

Event ID 4004

Event Type: Warning
Event Source: MSExchange Availability
Event Category: Availability Service
Event ID: 4004
Description:
Process xxxx[w3wp.exe:/LM/W3SVC/1/ROOT/xxxx]:
Unable to find a public folder server for organizational unit (OU) xxxx. The service will attempt to find a random server, which may take a longer time to service the request.

The Exchange Server 2007 Availability Service cannot search through all the public folder stores if an organization has more than 100 public folder stores. Therefore, the free/busy information is not retrieved for all users.

To resolve this problem, follow these steps:

1. Install Update Rollup 2 for Exchange Server 2007 Service Pack 1. For more information about Update Rollup 2 for Exchange Server 2007 Service Pack 1, see the following Exchange Help topic:
   Description of Update Rollup 2 for Exchange Server 2007 Service Pack 1
   For more information about how to install the latest Exchange service pack or update rollup, see the following Exchange Help topic:
   How to Obtain the Latest Service Pack or Update Rollup for Exchange 2007
2. Locate the Web.config file in the following folder:
   %ProgramFiles%\Microsoft\Exchange Server\ClientAccess\Owa
3. Open the Web.config file in Notepad, and then locate the following line between the <appsettings> segment and the </appsettings> segment:
   <add key="MaximumDatabasesInQuery" value="250" />
   
   Note If this line does not exist between the <appsettings> segment and the </appsettings> segment, insert the line.
   
   Note The value of the MaximumDatabasesInQuery key indicates the number of public folders that must be available for your organization. The default value is 100.
   
4. Save the Web.config file.
5. Perform steps 3 through 5 to make the same change to the Web.config file in the following folder:
   %ProgramFiles%\Microsoft\Exchange Server\ClientAccess\EWS

Note The change that is made to the Web.config file in the Owa folder makes sure that you see the free/busy information in Microsoft Office Outlook Web Access. The change that is made to the Web.config file in the EWS folder makes sure that you see the free/busy information in Microsoft Office Outlook 2007.

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